Adding browser notifications

You can turn browser notifications on in the users page.
![2](https://f.cloud.github.com/assets/60162/407029/b567e1c0-aad4-11e2-8e9b-35bd860d006f.png)


after that you will get these kind of notifications
![3](https://f.cloud.github.com/assets/60162/407030/cdd88048-aad4-11e2-8023-92b5b0172dc0.png)

which also shows up here
![4](https://f.cloud.github.com/assets/60162/407032/db3aa39c-aad4-11e2-97d1-899d41998ec0.png)

Trello card:
https://trello.com/c/00HgcRSs