Solve Issue#31: Provide Notifications for new Error Reports

Now with this, each developer will be notified whenever a new Error Report is generated.
On each page, number of *unread* notifications will be displayed.
![Alt text](http://dhananjay92.files.wordpress.com/2014/07/screenshot-notification-count.png?w=842 "Notifications on Nav Panel")

Notifications Page displays All the Pending Notifications.
![Alt text](https://dhananjay92.files.wordpress.com/2014/07/screenshot-notification-page.png "Notifications Page")

TODO: 
 - [ ] Add the test cases for `Notification` Model & Controller.