XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Move XWikiServerClassDocumentInitializer from oldcore to wiki-default
* Create xwiki-script
* First version of the API and of the implementation.
XWIKI-9516: Merge xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Create xwiki-platform-wiki-template modules.