Update control

- imagemagick and patchelf might be removed from Build-Depends if debian/rules is being reworked.
- I've added gstreamer0.10-plugins-bad and gstreamer0.10-plugins-ugly to nightingale Depends, which might be reverted (I personally prefer all gstreamer plugins installed at once).
- nightingale-unity-integration is a seperate package that contains only the Unity integration plugin. Since I'm not a Unity user, I didn't test if nightingale + nightingale-unity-integration works.
- Slightly different package descriptions.