Intended to fix issues raised in #2681.
Changes up the tri-layout tabs, and the main header menu toggle,
to be buttons while adding better text and keyboard controls.
Updated the component format of a few elements along the way.
- Set proper semantic tags for main parts of content.
- Removed focus-trap from tag manager/autosuggest.
- Set better accessibility labelling on tag manager.
- Updated collapsible sections to be keyboard navigatable.
- Improved input focus styling to better fit theme.
- Updated custom styled file picker to be accessible via keyboard.
Related to #1320
