Refactor the way that `Button` components are styled

Handling any deviation from default styling of `Button` components
has been painful, and these changes make it an all or nothing affair:
the `Button` component will apply default styling only in the absence
of a `className` prop. When a `className` prop is present, that will
supersede any component default styling.

These changes make button SCSS mixins clearer and easier to reuse and
extend.

`usePrimaryStyle`, `useCompactStyle`, `useInputStyle` props removed
from `Button` in preference of mixins to reduce `Button` complexity and
confusion over CSS precedence.

Components that use `Button`, and their styles, have been updated here
as needed.

Bump sass from 1.26.7 to 1.26.8

Bump @sentry/browser from 5.15.5 to 5.17.0

Bump postcss from 7.0.31 to 7.0.32

Bump puppeteer from 3.2.0 to 3.3.0

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.31 to 7.0.32.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/7.0.31...7.0.32)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.687.0 to 2.691.0.
- [Release notes](https://github.com/aws/aws-sdk-js/releases)
- [Changelog](https://github.com/aws/aws-sdk-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js/compare/v2.687.0...v2.691.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 17.9.2 to 17.11.0.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v17.9.2...v17.11.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [sass](https://github.com/sass/dart-sass) from 1.26.7 to 1.26.8.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sass/dart-sass/compare/1.26.7...1.26.8)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 5.15.5 to 5.17.0.
- [Release notes](https://github.com/getsentry/sentry-javascript/releases)
- [Changelog](https://github.com/getsentry/sentry-javascript/blob/master/CHANGELOG.md)
- [Commits](https://github.com/getsentry/sentry-javascript/compare/5.15.5...5.17.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [puppeteer](https://github.com/puppeteer/puppeteer) from 3.2.0 to 3.3.0.
- [Release notes](https://github.com/puppeteer/puppeteer/releases)
- [Commits](https://github.com/puppeteer/puppeteer/compare/v3.2.0...v3.3.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

If an event is triggered from a link or button or a descendent of a link or button, then prevent scrollToAnnotation from firing. It is assumed in these cases that a more specific action was intended and the page shall not scroll to the underlying annotation. Additional, dom-element.js has moved to /shared since its now used in both the annotator and sidebar 

Bump postcss from 7.0.30 to 7.0.31

Merge pull request #2216 from hypothesis/dependabot/npm_and_yarn/karma-coverage-istanbul-reporter-3.0.3

Bump karma-coverage-istanbul-reporter from 3.0.2 to 3.0.3

Bump sass from 1.26.5 to 1.26.7

Bumps [@babel/preset-react](https://github.com/babel/babel/tree/HEAD/packages/babel-preset-react) from 7.9.4 to 7.10.1.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.10.1/packages/babel-preset-react)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/preset-env](https://github.com/babel/babel/tree/HEAD/packages/babel-preset-env) from 7.9.6 to 7.10.2.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.10.2/packages/babel-preset-env)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/core](https://github.com/babel/babel/tree/HEAD/packages/babel-core) from 7.9.6 to 7.10.2.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/commits/v7.10.2/packages/babel-core)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump puppeteer from 3.1.0 to 3.2.0

Bump axe-core from 3.5.3 to 3.5.4

Bumps [postcss](https://github.com/postcss/postcss) from 7.0.30 to 7.0.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/7.0.30...7.0.31)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.683.0 to 2.687.0.
- [Release notes](https://github.com/aws/aws-sdk-js/releases)
- [Changelog](https://github.com/aws/aws-sdk-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js/compare/v2.683.0...v2.687.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [sass](https://github.com/sass/dart-sass) from 1.26.5 to 1.26.7.
- [Release notes](https://github.com/sass/dart-sass/releases)
- [Changelog](https://github.com/sass/dart-sass/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sass/dart-sass/compare/1.26.5...1.26.7)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [axe-core](https://github.com/dequelabs/axe-core) from 3.5.3 to 3.5.4.
- [Release notes](https://github.com/dequelabs/axe-core/releases)
- [Changelog](https://github.com/dequelabs/axe-core/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/dequelabs/axe-core/compare/v3.5.3...v3.5.4)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [puppeteer](https://github.com/puppeteer/puppeteer) from 3.1.0 to 3.2.0.
- [Release notes](https://github.com/puppeteer/puppeteer/releases)
- [Commits](https://github.com/puppeteer/puppeteer/compare/v3.1.0...v3.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [karma-coverage-istanbul-reporter](https://github.com/mattlewis92/karma-coverage-istanbul-reporter) from 3.0.2 to 3.0.3.
- [Release notes](https://github.com/mattlewis92/karma-coverage-istanbul-reporter/releases)
- [Changelog](https://github.com/mattlewis92/karma-coverage-istanbul-reporter/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mattlewis92/karma-coverage-istanbul-reporter/compare/v3.0.2...v3.0.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Tidy/Organize existing SASS color variables

Standardize text colors

- Also tighten padding as it was a little loose