Select/deselect twunch cell on viewWillAppear/viewWillDisappear

Before:
![before](https://cloud.githubusercontent.com/assets/357846/2886404/4121f356-d4e4-11e3-9b74-25545ada8848.gif)


After:
![after](https://cloud.githubusercontent.com/assets/357846/2886407/4a05d730-d4e4-11e3-8a5e-8e70f63740e4.gif)