Remove unroll and convert its use cases to use forEach instead

`unroll()` is not necessary to maintain as it didn't offer any value when writing tests over a simple `forEach()` call over a list of test parameter sets for a common testing function.

Make it easier to test client from a different device

Bump preact from 10.0.0 to 10.0.1

Make it easier to test the development client from a different device by removing
the need to customize the `SIDEBAR_APP_URL` and `PACKAGE_SERVER_HOSTNAME`
environment variables first.

Instead of hardcoding the client/h dev server hostname and scheme in the client's
boot script, support a very simple URL templating scheme where
references to `{current_host}` and `{current_scheme}` are replaced by
the corresponding elements of the boot script's URL.

This means that for example, if the embed script is accessed as
https://Roberts-MacBook-Pro.local:5000/embed.js then the boot script
will use asset URLs such as
https://Roberts-MacBook-Pro.local:3001/assets/sidebar.bundle.js. If
the boot script is accessed as http://localhost:5000/embed.js then
it will generate http://localhost:3001/assets/sidebar.bundle.js
instead.

A related change in h will remove the need to set the `CLIENT_URL` env
var and modify the OAuth client's redirect URL. At present, those steps
are still required.

Bump mocha from 6.2.1 to 6.2.2

Bump @sentry/browser from 5.7.0 to 5.7.1

Bump karma from 4.3.0 to 4.4.1

Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.0.6 to 2.0.7.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](https://github.com/cure53/DOMPurify/compare/2.0.6...2.0.7)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [karma](https://github.com/karma-runner/karma) from 4.3.0 to 4.4.1.
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](https://github.com/karma-runner/karma/compare/v4.3.0...v4.4.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@sentry/browser](https://github.com/getsentry/sentry-javascript) from 5.7.0 to 5.7.1.
- [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/5.7.0...5.7.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [preact](https://github.com/preactjs/preact) from 10.0.0 to 10.0.1.
- [Release notes](https://github.com/preactjs/preact/releases)
- [Commits](https://github.com/preactjs/preact/compare/10.0.0...10.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.549.0 to 2.553.0.
- [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/v2.549.0...v2.553.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [mocha](https://github.com/mochajs/mocha) from 6.2.1 to 6.2.2.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mochajs/mocha/compare/v6.2.1...v6.2.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Convert markdown editor 3/3 - Convert editor and improve toolbar UX

Move the utility function to the top of the file so that all the
components are grouped together.

Also reformat `markdown-editor-test.js`.

 - Remove `user-select` rule. This is no longer needed because the
   toolbar buttons are `button` elements rather than `i` elements
   (which have selectable text)
 - Simplify border rules
 - Use CSS color name instead of a variable for consistency within the
   file

This has been replaced by the `MarkdownView` and `MarkdownEditor`
components.

Convert the editor part of the `<markdown>` component to Preact.

 - Remove the `readOnly` input as this mode is now handled by the
   separate `MarkdownView` component
 - Improve toolbar a11y by:
   - Adding the "toolbar" ARIA role and an aria-label to the toolbar container
   - Using `button` elements for toolbar buttons
   - Increasing the hit target area for buttons
 - Improve toolbar styling by:
   - Using flexbox
   - Using the modern color palette
   - Fixing the padding around the preview output

Convert markdown editor 2/3 - Convert markdown viewer

Convert markdown editor 1/3 - Remove "enabled" state from excerpt component

Convert the view mode of the markdown editor (when `readOnly` is `true`) to Preact.
The edit mode (when `readOnly` is `false`) will become a separate
component.

Simplify the `<excerpt>` component by removing the `enabled` property.
This property was used to avoid the markdown editor being truncated when
rendered inside the excerpt. However it is possible to achieve the same
result without this property by using `ng-if`.

This change will simplify porting the excerpt component to Preact and
also paves the way to splitting the existing `<markdown>` component into
two separate, simpler, components: One for the "view" mode and one for the "edit"
mode.

Bump @sentry/browser from 5.6.3 to 5.7.0

Revert "Improve accessability for toggle buttons"

This reverts commit ab3d902f.

This change caused the client to fail to load on pages where
`window.hypothesisConfig` is not defined.

Bump scroll-into-view from 1.9.7 to 1.11.0

Bump core-js from 2.6.9 to 2.6.10

Bump autoprefixer from 9.6.4 to 9.6.5

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.6.4 to 9.6.5.
- [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/9.6.4...9.6.5)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>