Introduce xwiki-enterprise-ui-mainwikipreferences and stop duplicate XWikiPreferences in xwiki-enterprise-ui-wiki

Currently, xwiki-enterprise-ui-wiki has it own XWikiPreferences because the default rights are different in a subwiki than in the main wiki. But every time a modification is made on XWikiPreferences on the main wiki, we must also do it for the subwiki. And we often forget to do it.

A better practice is to stop duplicate the document but instead inheriting it from the main wiki and modify the default rights with the xar transformation plugin.

I also propose to create a module called "xwiki-enterprise-ui-mainwikipreferences" that would store only XWikiPreferences because XWikiPreferences has nothing to do in "xwiki-enterprise-ui-admin-user".