Style notifications with a Bootstrap row

Closes #2112 

Fix styling bug of each delete button appearing further to left than the previous one

Make styling more semantic using classes and separate stylesheets

I see some other things I could maybe try to do later to further adjust the styling but for now this is just a minimal PR to fix the immediate user-facing bug.

Wide screen:
![new_full_screen](https://cloud.githubusercontent.com/assets/5103414/5425156/492aefc8-82d9-11e4-90bd-f22dce898f19.png)

Narrow screen:
![narrow_screen](https://cloud.githubusercontent.com/assets/5103414/5425157/4b326cd8-82d9-11e4-9d66-784075cbc8e5.png)