Feature/ap sidebar improvements

* Adds active state for sidebar navigation
* Tweaks the collapsing animation

**Before**
http://cl.ly/image/1S0r103W000C/download/Screen%20Recording%202014-12-11%20at%2011.16%20am.gif

**After**
http://cl.ly/0C2j3u090e3S/download/Screen%20Recording%202014-12-11%20at%2011.17%20am.mov