XWIKI-8696: Search suggestions for the "User Name" field from the "Workspace Users" administration page don't appear correctly
* Merge the changes done to XWiki.XWikiGroupSheet for XWIKI-4022 (Improve users/groups list field displayer) in XWiki.WorkspaceUsers
* Add the ability to add/invite multiple users as once.
* Remove the custom XWiki.XWikiGroupSheet from the workspace template (some features were not working and keeping it synchronized with the original version is hard).