Improve tabs styling

Improve the styling of navigation tabs to match the wireframes at
http://people.redhat.com/~jcoufal/openstack/horizon/details/2014-02-19_details.pdf

Partially implements: blueprint detail-pages-ia

Change-Id: I425e74361ba231403d72627c06c29c311959f152
Extend height of nav accordion

Change-Id: I2b7381e8f8a10e9b35737fac456e2796829fcf00
Closes-Bug: #1365680
After cherry picking the fix to grow the navigation bar to fill the screen
... this minor change sets the background of the un-used area to be
light grey