replace the clock icon by a proper contactlist icon

I've let the clock icon inside the repository for now since it seems that we'll need it in the future. Let me know if you think that's better to remove it.

I've also replaced the old icons with the new ones, in general.

![talkilla_userlist](https://f.cloud.github.com/assets/67073/2085620/97ca614e-8e48-11e3-944e-ae664b9768dd.jpg)