Try to fix #6 (closed) and #5
MPV: Don't load the video by default, force the user to click on the button to avoid some strange race conditions
The race condition between Qt's widget creation and mpv getting the WID doesn't seem to be fixed for now, will need to investigate further.
MPV: Use mpv_destroy to delete the player, don't use the "quit" command as it seems to be the way recommended in the client.h header
Try to force the window creation before passing the WID to MPV to fix the possibility where the window is not already created and thus everything crashes.
