diff widgets/Fader.cpp @ 133:9e6b3e239b9d

* Add zoom thumbwheels to Pane.  Implement horizontal thumbwheel, and
  vertical depending on layer type (supported for waveform and spectrogram,
  though wrong for log-scale spectrogram at the moment).
* Add bare bones of a spectrum layer.
* Add window icon
* Add shortcut for "insert time instant" on laptops without keypad enter (";")
* Delete FFT processing thread when it exits (at least, next time we're asked
  for something interesting)
* Get audio file extensions from the file readers, and thus from libsndfile for
  the wave file reader -- leads to rather a wide combo box in file dialog though
* Better refresh order for spectrogram (redraw centre section first)