* 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)