Create an improved Navigation Panel for displaying the XWiki server structure

Currently the navigation panel is a global non-modal window used for all opened documents.

The new navigation panel, must respect the following rules:

• every document can have its own navigation panel
• the navigation panel must be unique in a document
• the navigation panel should be in a child frame of the document frame - the resize, move , close events of the main document must be applied on the navigation panel

After this is done, remove the hack for the "Add Space" dialog position