Convert tabs to pills

https://issues.sonatype.org/browse/NEXUS-7709

This is a work in progress. A few items still to be resolved:

+ Changes don’t propagate to tabs in modals
+ The button placement (above the tabs) is still horrible, and I’m trying to find a better place for them.

Before:
http://take.ms/a8mws

After:
http://take.ms/kuGaO