DIMITRI: Header subnavigation fixes.

This makes the subnav work on Angular and Django pages. Hacky, but good enough for now.

![screen shot 2014-09-19 at 7 09 30 pm](https://cloud.githubusercontent.com/assets/137158/4343944/51b3d73c-406b-11e4-9873-b2192591413c.png)

Yep -- $watch evaluates the expression after every $digest. The expression should be cheap, of course. Also, it shouldn't affect much state -- Angular calls $digest 10 times or so and, if state is still dirty afterward, throws an error.