New notification icons

This PR closes #24 by porting the new launcher icon design to the notification icons.

### Before
![ic_stat_notification_old](https://cloud.githubusercontent.com/assets/153802/4762210/1c3b041e-5aff-11e4-9e04-bbd2deb7c76c.png)

### After
![ic_stat_notification_new](https://cloud.githubusercontent.com/assets/153802/4762213/1e03b3ae-5aff-11e4-9e31-ae2563716eed.png)