* Implement play mute, level and pan controls and a layer visibility control * Handle swapping the buffers in AudioCallbackPlaySource more gracefully, so that in many cases it can be done inaudibly. Still gets it wrong when playing in a noncontiguous selection. * Fix to SV file save for non-2d sparse models * Fixes to LED button drawing and AudioDial mouse functionality * Add progress bar for Ogg file import * Reshuffle PropertyContainer and its subclasses so it can be a QObject * Add layer dormancy (invisible layer permitted to free its cache space) * Optimisations to SpectrogramLayer, removing locks when reading/writing individual pixels in the cache (should be unnecessary there) -- there's still an issue here as we need a lock when reading from the model in case the model is replaced, and we don't currently have one * Several munlock() calls to make it harder to exhaust real memory if running in an RT mode with mlockall() active