XWIKI-9475: Change top menus when Workspaces is activated.

* New menu.
* Renamed "Wiki Directory" and "User Directory" to "Wiki Index" and "User Index".
* Use the house icon for the Home.
Merge pull request #168 from gdelhumeau/XWIKI-9475

XWIKI-9475: Change top menus when Workspaces is activated