Changes

• DBus: Fetch playback progress when position is queried (fixes #223, #236)
• DBus: Fix trackid replacing string with d-bus path, Seek & SetPosition implementation (#252)
• Add notifications (#247)
• Do not delete from empty queue (fixes #253)
• Make contextmenu aware of commands (e.g. for Vim-like bindings) (fixes #108, #157, #178, #199, #250)
• Use libc for setlocale() to fix non-ASCII (#256)