Preliminary port to gtk3, gst1.0

Here is a preliminary port to GTK3 and GStreamer 1.0. I've been running it for a few months without any glitches.

TODO:

1. Test and fix the indicator applet. I can't test it here.
2. Fix Debian package dependencies (I don't run debian).
3. Port python-dbus to gdbus
4. Port to python3?

I made the pull request against master but you should probably pull to a separate branch.

Note: The `*.ui` files have large diffs because I basically just opened them up in glade and re-saved them to port them.