A more adaptative layout for the chat window

(sorry for the ugly faces)

Default

![capture decran 2013-07-17 a 16 17 35](https://f.cloud.github.com/assets/41547/812193/f94226d4-eeeb-11e2-98e4-a156c359fa54.png)

Popped up (medium sized)

![capture decran 2013-07-17 a 16 18 31](https://f.cloud.github.com/assets/41547/812202/062b091a-eeec-11e2-896c-84facecad76d.png)

Popped up (larger)

![capture decran 2013-07-17 a 16 18 49](https://f.cloud.github.com/assets/41547/812207/107edefa-eeec-11e2-8353-aa5fed45e75c.png)

Full screen (13" mba)

![capture decran 2013-07-17 a 16 19 55](https://f.cloud.github.com/assets/41547/812209/19a515f8-eeec-11e2-8a42-b741f00e3110.png)