Improve notifications and conversations views design on mobile

Small improvements to the conversation and notification views on mobile

Before:
![conversation-before](https://f.cloud.github.com/assets/930064/1556117/9545a0a2-4eae-11e3-8580-bd8e22e7600b.png)
After: 
![conversation-after](https://f.cloud.github.com/assets/930064/1556116/8c2f2aba-4eae-11e3-85ef-39530352dff8.png)

Before:
![notification-before](https://f.cloud.github.com/assets/930064/1556118/9d733b72-4eae-11e3-9955-3e1d9dcaf8dc.png)
After:
![notification-after](https://f.cloud.github.com/assets/930064/1556120/d226a264-4eae-11e3-9eda-0b85f27a1d29.png)