Monstro changes

Quick summary:
- added a reverse sync mode. This syncs the oscillators by, instead of resetting phase, inverting the waveform at each sync. Both sync modes can be combined, which can produce interesting effects.
- removed the foolery with amp delta (except the one on the pw osc) as it's quite ineffective, and instead added a simple first-order integrator to the master... may add an on/off switch or control knob for that later if it seems one is needed.
- added a "smooth random" waveform for the LFO's... this is like the random waveform but interpolated so the changes are gradual instead of sudden.

Btw @tobydox, I'd like to make the bandlimited waveform generation use pre-generated waveform files so that they wouldn't need to be generated again in every session, which causes a delay of several seconds... the runtime generation could then function as a fallback only. I'd also like the pre-generated files to be provided with LMMS. But I'm not sure where to put them, and how to make it so LMMS knows where they are regardless of install prefix... is the share/lmms directory ok?