Summary: Make tabs do stuff when you click 'em.
Test Plan:
- Clicked object box tabs in UIExample.
- Viewed some existing non-tab UIs (Differential, Maniphest).
- Viewed some existing non-tab, multiple-list UIs (Diffusion).
- Grepped for methods I changed.
Reviewers: chad, btrahan
Reviewed By: chad
CC: aran
Differential Revision: https://secure.phabricator.com/D7361
