Add notifications, tray and new tag

Created by: kajzersoze

First I just want to say that I love this app, great job !

Now, I've added few things that I was missing, like tray option and closing to tray, there is a option to turn that feature off, in tray itself on right click there are options to Play / Pause and Quit. Left click will bring the main window back if it was closed to tray. Second thing is notifications when station change to a new song. Third thing is a new TAG , some stations provide url for the art from the front cover of the album that is playing in homepage TAG, example of that is in the attached picture, station is Radio Paradise. If there's no art in that TAG then standard station icon will show instead.

Also, you forgot to load window positions from gsettings, so that's added as well :)