XWIKI-9456: After the creation of a new (sub)wiki, the Distribution Wizard should not appear.

* Change some fields to "protected" in order to make it easier to extend.
* It's needed for the 5.2 migrator, and it can ve reverted for 5.3
* See: https://github.com/xwiki/xwiki-enterprise/pull/45
Merge pull request #167 from gdelhumeau/XWIKI-9433

XWIKI-9456: After the creation of a new (sub)wiki, the Distribution Wizard should not appear.