Refactor and cleanup

* Cleaned up unused templates
* Refactored to use Zendesk Apps requests API
* Refactored agent reply filtering logic to use underscore.js
* Fix problem where button disappears after modal is closed
* Smaller widget layout to save space in the sidebar

![image](https://cloud.githubusercontent.com/assets/1028921/4905843/c45004b2-6453-11e4-97e2-efc23f67c7b3.png)

* Clearer text and taller textarea on modal

![image](https://cloud.githubusercontent.com/assets/1028921/4907820/8c9c000a-6464-11e4-8702-754ff66a7827.png)