Added support to edit / delete issue comments.

Added ability to edit / delete individual issue comments. 
 - Reused existing drawables and should be replaced with proper state list drawable.

![screen](https://cloud.githubusercontent.com/assets/4177515/2751079/dda03022-c8ae-11e3-800e-d5db3a538ed8.png)

**Edit Comment**
![screen2](https://cloud.githubusercontent.com/assets/4177515/2751077/dd95b188-c8ae-11e3-9048-0e1aecd6645f.png)

**Delete Comment**
![screen3](https://cloud.githubusercontent.com/assets/4177515/2751078/dd9a6b06-c8ae-11e3-91f1-0269449e1741.png)