Made another mass of accessibility improvements

- 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

resources/views/comments/comments.blade.php

@@ -1,4 +1,4 @@
-<div page-comments page-id="{{ $page->id }}" class="comments-list">
+<section page-comments page-id="{{ $page->id }}" class="comments-list" aria-label="{{ trans('entities.comments') }}">
 
     @exposeTranslations([
         'entities.comment_updated_success',
@@ -34,4 +34,4 @@
         @endif
     @endif
 
-</div>
+</section>