XWIKI-9412: Add a UI to handle the new "SubWiki Creation" right in the Administration.

* I have added a MultiWikis page in the General section of the Administration
* In this page, you have a message if workspace-template is not installed.
* In this page, you can set who has the SUBWIKI_CREATION right.
* The template rightsUI.vm has been modified to handle this new page.
XWIKI-9412: Add a UI to handle the new "SubWiki Creation" right in the Administration.

* Rename admin.multiwikis.* to admin.subwikis.*
XWIKI-9412: Add a UI to handle the new "SubWiki Creation" right in the Administration.

* Rename "MultiWikis" to "Subwikis".
* Set "Subwikis" in first position inside the "Configuration" section.
XWIKI-9412: Add a UI to handle the new "SubWiki Creation" right in the Administration.

* Move XWiki.AdminSubWikisSheet from xwiki-platform-administration-ui to xwiki-platform-workspace-ui
* Add a ConfigurableClass to it instead of hacking XWiki.AdminSheet
** Because of this, the Subwiki section will be at the bottom of the "Application" section instead of being in the first position of "General".
** It will be fixed when we will use UI Extension Point instead of ConfigurableClass in the Administration.
XWIKI-9412: Add a UI to handle the new "SubWiki Creation" right in the Administration.

* Move some translations from ApplicationResources.properties to WorkspaceManager.Translations.
XWIKI-9412: Add a UI to handle the new "Wiki Creation" right in the Administration.

* Rename "subwiki" to "wiki".
XWIKI-9412: Add a UI to handle the new "Wiki Creation" right in the Administration.

* Fix a warning message that was displayed in the console.
Merge pull request #147 from gdelhumeau/XWIKI-9412

XWIKI-9412: Add a UI to handle the new "Wiki Creation" right in the Administration