Better User GUI

I have refactored the GUI of your plugin, i think now it fits better with rhythmbox.
I have also remove the button icon, it's something that you use only 1 time after configured. I dont think its worth have it that all time for an easy access. It only display in the menu now.

![Captura de tela de 2013-01-02 16:36:10](https://f.cloud.github.com/assets/677051/38950/6386318c-550b-11e2-8ba3-7fb783efac6c.png)