Menu improvements when Workspaces activated

This still needs to be discussed and approved in the community

Current proposals:
http://incubator.myxwiki.org/xwiki/bin/view/Improvements/PortalMenu
(another in working proposal)

Also make the Workspace creation step consistent with the Create Page, Create Space steps
'Main Wiki' menu entry take the value of the xwiki:Main.WebHome title (can be 'Home', 'Main Wiki', 'Portal', 'Intranet', etc.)