Enhancement: Accessibility improvements

A lot of random changes:
- Extracted some helper classes to ODS & unified their usage
- Removed `<br>` tags that were incorrectly used for spacing
- Used `<h4>` tags for headings in the files sidebar
- Make skip-to-main button translate-able
- Update searchbar label string
- Renamed "personal files" to "all files" in routes (soft rename, due to changes in the future)
- Updated ODS to v6.0.3, making row heights theme-able and bringing a more accessible avatar component that improves loading of users' profile pictures
- Translate quick action labels/tooltips properly
- Added a note about actions being available above the file list to the live region update for selection

https://github.com/owncloud/web/pull/4965
https://github.com/owncloud/web/pull/4975
https://github.com/owncloud/web/pull/5030
https://github.com/owncloud/web/pull/5088
