Chat: add extra padding for the roster

Related to https://github.com/diaspora/jsxc/pull/42

Before:
![before_closed](https://cloud.githubusercontent.com/assets/3798614/5150962/585ab5d0-71d8-11e4-8103-ed1e24ef2892.png)
![before_open](https://cloud.githubusercontent.com/assets/3798614/5150963/585b0b70-71d8-11e4-9846-a8ae2abe946b.png)
After:
![after_closed](https://cloud.githubusercontent.com/assets/3798614/5150966/6126c186-71d8-11e4-898e-9c271e6a992f.png)
![after_open](https://cloud.githubusercontent.com/assets/3798614/5150967/612734fe-71d8-11e4-830c-ae1eb2a357c8.png)
After, 1024px width:
![after_open_smalldevice](https://cloud.githubusercontent.com/assets/3798614/5150975/6d62e72c-71d8-11e4-89c1-7a32ee27992f.png)