Glade cleanup

Bug #51 (closed) seemed like an easy one to fix, but when I opened pavucontrol.glade in Glade, it complained about targeting gtk2, and additionally there were many changes done to the .glade file automatically just by opening and saving the file in Glade.

To avoid dealing with the automatic changes getting mixed with manual changes, I decided to commit the automatic changes separately. There were some object ID changes that caused crashing, so I had to adapt the code as well.

To clarify: this merge request doesn't fix bug #51 (closed), only the gtk version complaint and the automatic changes are dealt with.