XWIKI-14711: Adding a wiki descriptor after it's been deleted doesn't make the wiki appear in the wiki index

- Using color themes variables + fixing some spacing

- Have consistent Delete buttons messages. Deprecated the old keys
- Removed the glyphicon icon
- Removed docextra area
- Removed the bold text styling
- Used the new .btn classes

* Fix WebStandard tests.

* Fix the Wiki Templates section (the live table id was coliding with the menu id)
* Remove the whitespace from the start of the Google Analytics and Annotations sections.

* Improve the Wikis category and its sections.
* Rename "Template" in "Wiki Templates" and add help text
* Use the full width in the Descriptor section

* Fix the category sort (based on the specified 'displayBeforeCategory')
* Replace the 'Applications' category with 'Other'
* Reorder the categories based on their importance (Users & Groups, Extensions, Look & Feel, etc.)

This reverts commit 5f8c97f5.

This reverts commit c45249a5ce3696f0eadbf530eba74831c7de5433.

XWIKI-13969: Provide helper to make easier to migrate classes in mandatory documents