Change Add New Page button interaction.

Turn into a plugin.
Add cancel button.
Only collapse button when input is empty (unless on 'Cancel' click).

Fixes #437 

![screen shot 2014-03-06 at 9 17 05 pm](https://f.cloud.github.com/assets/96776/2354243/29cb5782-a5ba-11e3-8b1d-c57825f832b4.png)