XWIKI-9516: Create a new Wiki API that replaces xwiki-platform-wiki-manager and xwiki-platform-workspace.

New API!

* I am working on the "template" feature this week (by using WikiProvisioner).
* After 5.2M2, I will write a lot of functional & unit tests + fix bugs.
* Even if the implementation is not perfect, the most important is to valid the API.

I hope you like it!

Louis-Marie