Stopping or pausing playback doesn't completely stop the sound

[YuriSizov]

Originally reported here: TerryCavanagh/boscaceoil#40
Confirmed in 3.0-stable.

When you stop or pause the playback, by any means, there is still residual sound produced by the synthesizer. In the current dev build of 3.1 we correctly cut off the sound from notes, however global effects can still hang around for as long as they want.

There is probably a need for a proper solution on the GDSiON side of things, but we can also look for a way to patch this in Bosca itself. It boils down to us being able, or not, to reset the effector somehow. If the appropriate API is not exposed, we could try quickly removing all effects on stop/pause, and immediately restoring them.