new navbar.css, html pages and css refactored

A newbar.css file has been included.
The html pages now have the navbar.css link included.
The css's from the html pages doesn't have classes related to the navbar
anymore.
qubal_prerender.py -> A new parameter has been included to "read" the
current user level.
views.py-> the new paramenter current_level is included in the function
calls.