XWIKI-11940: Make internal the classes and interfaces of the LESS Module that should not have been public and refactor bad designed code.

* Fix checkstyle.

XWIKI-11940: Make internal the classes and interfaces of the LESS Module that should not have been public and refactor bad designed code.

* Removed the dot from the description (+ removed the "XWiki" part since everything is about XWiki)

* Change the description of the application in the pom.xml.

* Add a Skin Application
* Add an UI to easily add/edit/delete XWikiSkinFileOverrideClass objects

XWIKI-11715: JSX (SSX too?) gets executed twice if set to "On this page or on demand" and included manually
- Properly serialized the current document's reference when adding it in the set of skin extensions, thus properly deduplicating it when needed.

XWIKI-11763: Several wiki pages generated by Java code are still using the old deprecated way of including other pages

* Add the property "contentType" to the SSX objects
* SSX objects can handle LESS code
* Create Skin and Color Theme references
* Continuing the refactoring of the LESS module to be able to compile LESS resources that are not files
* Lot of tests done locally in addition of unit tests, that is why I allow myself to low down the jacoco requirement, with the ambition to write new tests in the following weeks.

* First implementation of SSX using LESS.
* Todo: a cache cleaner when a SSX is saved.

XCOMMONS-694: Automatically verify in the build that the component threading model is explicitly declared
* Fixed regression introduced when moving from @Component("xxx'") to @Named("xxx")

XCOMMONS-694: Automatically verify in the build that the component threading model is explicitly declared

This reverts commit c3134ed5.

This reverts commit 333e6ea1.

Reason: The release failed to build due to some dependency problems, so I`m restarting the release.

* Fixed renamed that failed locally

* Fix components.txt

* Done on the API side

* Improved translations (also updated on l10n for the French one)