Second level of XWiki virtualization

For now only MAIN wiki has the ability to run Workspace Manager and set up workspaces.
The proposal is to make "good old" virtual wiki to have this ability also.

-------| -> workspaces
Main | -> virtual wiki 1 -> workspaces
Wiki | ..................................................
-------| -> virtual wiki N - "Solo" - No Workspace Manager onboard and no links in top menu.

In scenario

• Main Wiki -> virtual wiki 1 -> workspaces

virtual wiki 1 and it's workspaces has independent (from Global users pool) pool of users.

Such a way we can run all scenarios simultaneously on the same XWiki instance.

See also http://jira.xwiki.org/browse/XEM-208 about programming rights incapsulation inside workspaces and virtual wikis.