XWIKI-9405: Add a "SubWiki Creation" right.

* Adding changes suggested by committers on the pull request.
** ALL_RIGHTS_EXCEPT_ADMIN renamed ALL_RIGHTS_EXCEPT_ADMIN_AND_SUBWIKI_CREATION.
** deprecatedContext renamed xcontext in DefaultWorkspaceManager#canCreateWorkspace()
** better use of Logger in DefaultWorkspaceManager#canCreateWorkspace()
** introduce $hasCreateSubwiki in xwikivars.vm

Thanks for the review!