ActionBar/ContextMenu visual fixes

Hello there! I've tweaked the ActionBar and ContextMenu CSS so they are more in line with the UX specs. I'll likely have some more patches coming, but this is a start.

Paul

![actionbar_updates](https://f.cloud.github.com/assets/667875/112714/0ac853f2-6b29-11e2-95c4-008a3d50d49f.png)