Moved playlist functionality mostly to the playlistWidget
This makes it simple for playlist-reordering. Basically mpv_handler deals with reading the directory and loading the playlist but the playlistWidget is a front-end which triggers mpv->PlayFile when things are supposed to play, else maniuplation of the list no longer depends on the index.
Merge branch 'master' into playlist-reorder

Conflicts:
	src/ui/mainwindow.cpp
Renamed customlistwidget to playlistwidget
Almost done with implementation
Various functionalities of the playlist work now just need to fix some details like playlist visibility, index selection on file load, initial indexing problems.
Merge branch 'master' into playlist-reorder

Conflicts:
	src/mpvhandler.cpp
	src/mpvhandler.h
	src/ui/mainwindow.cpp
Completed playlist-reordering functionality
Tiny fix to LoadFile before merge