Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- `app/controllers/api/v1/statuses_controller.rb`:
  Conflict due to upstream adding a new parameter (with_rate_limit),
  too close to glitch-soc's own additional parameter (content_type).
  Added upstream's parameter.
- `app/services/post_status_service.rb`:
  Conflict due to upstream adding a new parameter (rate_limit),
  too close to glitch-soc's own additional parameter (content_type).
  Added upstream's parameter.
- `app/views/settings/preferences/appearance/show.html.haml`:
  Conflict due to us not exposing theme settings here (as we have
  a different flavour/skin menu).
  Took upstream change, while still not exposing theme settings.
- `config/webpack/shared.js`:
  Coding style fixes for a part we have rewritten.
  Discarded upstream changes.

app/javascript/mastodon/features/compose/components/poll_form.js

@@ -155,6 +155,7 @@ class PollForm extends ImmutablePureComponent {
         <div className='poll__footer'>
           <button disabled={options.size >= 5} className='button button-secondary' onClick={this.handleAddOption}><Icon id='plus' /> <FormattedMessage {...messages.add_option} /></button>
 
+          {/* eslint-disable-next-line jsx-a11y/no-onchange */}
           <select value={expiresIn} onChange={this.handleSelectDuration}>
             <option value={300}>{intl.formatMessage(messages.minutes, { number: 5 })}</option>
             <option value={1800}>{intl.formatMessage(messages.minutes, { number: 30 })}</option>