Create bell right before ringing/Fix Gst leak

For some reason MediaFile leaves after it's destruction Gst instances which hold fd to ringtone file. And after creating and destroying enough amount of MediaFile instances, fd count rises so high that it surpasses limit of fd per process and the app crashes. But if we close `media_file` manually in `stop ()` function, Gst* stuff is destroyed.

Also now we are "lazy" loading ringtones instead of keeping it in memory until alarm is deleted.