diff widgets/Thumbwheel.cpp @ 312:6de6f78b13a1

* Make it possible to drop audio files, layer files, session files and images
  onto SV panes.
  Need to do a bit more work on where we expect the dropped file to go,
  particularly in the case of audio files -- at the moment they're always
  opened in new panes, but it may be better to by default replace whatever is
  in the target pane.