new features: view main window, genre/rating, skip back 15, & some genres

While not fully cleaned up, there were a few things that bugged me: one was that if I closed the main window I would have to quit and relaunch. So instead, I disabled the close button and added a window menu. Also, if I was playing a track I wanted to be able to skip back 15s and  see the Genre and Rating, if any. So, I added these along with a few other Genres that I listen to. Nothing fancy, but more usable in general, IMO.