Only CCLA admins can see Manage Contributors tab.
Make CCLA sig viewing read-only for non-admins.

Only admins of CCLA organizations should be able to update (re-sign) CCLA
organization signatures. You don't want any old Bart Fart going in and making
your phone number something dumb like 1-800-OMG-BUTT or something right?!?!
Increase the tab margin bottom override.

In Firefox on Ubuntu, the line was still showing under the active tab. This
fixes that!