Bump autoprefixer from 9.7.0 to 9.7.1

Clean up `TopBar`: CSS, ARIA

Add Copy-version-details to help panel; tighten design/layout

Bump showdown from 1.9.0 to 1.9.1

Bump sass from 1.23.1 to 1.23.3

Bump preact from 10.0.4 to 10.0.5

Bumps [preact](https://github.com/preactjs/preact) from 10.0.4 to 10.0.5.
- [Release notes](https://github.com/preactjs/preact/releases)
- [Commits](https://github.com/preactjs/preact/compare/10.0.4...10.0.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump prettier from 1.18.2 to 1.19.1

Bumps [@babel/preset-env](https://github.com/babel/babel) from 7.6.3 to 7.7.1.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.6.3...v7.7.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Merge pull request #1490 from hypothesis/dependabot/npm_and_yarn/babel-plugin-mockable-imports-1.5.2

Bumps [@babel/preset-react](https://github.com/babel/babel) from 7.6.3 to 7.7.0.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.6.3...v7.7.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [babel-plugin-mockable-imports](https://github.com/robertknight/babel-plugin-mockable-imports) from 1.5.1 to 1.5.2.
- [Release notes](https://github.com/robertknight/babel-plugin-mockable-imports/releases)
- [Changelog](https://github.com/robertknight/babel-plugin-mockable-imports/blob/master/CHANGELOG.md)
- [Commits](https://github.com/robertknight/babel-plugin-mockable-imports/compare/v1.5.1...v1.5.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.7.0 to 9.7.1.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/compare/9.7.0...9.7.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [showdown](https://github.com/showdownjs/showdown) from 1.9.0 to 1.9.1.
- [Release notes](https://github.com/showdownjs/showdown/releases)
- [Changelog](https://github.com/showdownjs/showdown/blob/1.9.1/CHANGELOG.md)
- [Commits](https://github.com/showdownjs/showdown/compare/1.9.0...1.9.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [sass](https://github.com/sass/dart-sass) from 1.23.1 to 1.23.3.
- [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/1.23.1...1.23.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@babel/core](https://github.com/babel/babel) from 7.6.4 to 7.7.2.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.6.4...v7.7.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [prettier](https://github.com/prettier/prettier) from 1.18.2 to 1.19.1.
- [Release notes](https://github.com/prettier/prettier/releases)
- [Changelog](https://github.com/prettier/prettier/blob/master/CHANGELOG.md)
- [Commits](https://github.com/prettier/prettier/compare/1.18.2...1.19.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

- Tighten panel subheader and sub-panel navigation links
- Make vertical and horizontal rhythm consistent

By changing the temporary element for holding text from a `span` to a
`pre`, line breaks in formatted strings may be retained when copying
to the clipboard

NB: This change cannot be directly tested

Separate `asEncodedURLString` into two constituent methods, allowing
access to an un-encoded `asFormattedString`, which returns a string
formatted for (e.g.) copying to the clipboard.

Replace Help and Tutorial panels with single, preact panel

Improve tab bar accessibility

Help & Tutorial 4/n: Add support for status-change callback to `SidebarPanel`

Help & Tutorial 3/n: Refactor how auto-display of tutorial is determined

Setting an `ariaSelected` prop works in the latest Safari because elements have
an `ariaSelected` property as part of the Accessibility Object Model
implementation [1]. This is not yet implemented in Chrome however, so
the `ariaSelected` prop gets mapped to an `ariaselected` attribute. We
need to set the `aria-selected` attribute however.

[1] https://github.com/WICG/aom/blob/gh-pages/explainer.md#reflecting-aria-attributes

Update mobile testing docs

Add screenshot to clarify what change the developer might need to make.

Make boot URL templating work in IE 11 / early Edge