Start port to GTK using GIR

As the use of the tray icon in wxWidgets seems a bit problematic, as the icon
disappears, or is put as some kind of special window instead of the taskbar, I
presume in case the notification area hasn't started yet.

This, little, issues drove me to look a bit more to GTK. Benefits are it
supports more languages, and it's a native library. Downside could be it's
less portable, but the question is if it portable anyway at the moment, as
unison requires SSH, which is, according to their website, a bit problematic on
Windows.

And, I myself, wouldn't do much for it anyway, as I don't run it, and it would
be a big, and quite impossible (without running Windows), task to support it.

And, I've got to say, I quite like the API, at the moment. And, I'm happy that
it supports handling the default system icons, which makes things easier for me.
The result will be better then it was using wxWidgets, and I doubt if there are
some real downsides to the new approach, as, well, it seems to me like the only
downgrade is regarding Windows, and I don't care about that.
Make unisister command
Added popup menu

I should look into this, as I found out that since GTK 3.10, menu items with
icons have become deprecated. So I should consider using PyGTK, or finding an
other way to show a menu item with icon, accept the lack of icons or ignore the
deprecated state ...
Menu + about added
Put backends in separate file
Parse config files and start timer
Start separating model from view
Separate controller from view
Write unison backend
Interpret the unison output
Finish backend
Backend fixed
Little cleanup
Show message when done

The conversion is now complete, except from the preferences editor, but I don't
care.

Note GObject.thread_init(). I've been debugging quite a long time before I
realized the only reason it didn't work was GTK.

Anyway, I'm happy with the result, and the GUI is completely separated with the
actual logic, which should make it quite easy to convert to Qt, if I finally
decide to do so.
Merge branch 'gtk3'

Conflicts:
	unisister.py