simple solution for spatialization with SC, without SSR. segments fade in and pan from the peer's position (random) to the centre. in need of refactoring.
towards more flexible spatilization with SC, without SSR.

Merge branch 'sc_spatialization'

Conflicts:
	orchestra.py
recovered flat envelope for normal non-looped playback, which was unintentionally (?) changed to fade-out when looping was introduced in 7dd6552e (the fade-out was probably only supposed to apply for looped playback with \loop)
added SC mode for rear-to-front panning with 4 channels (no left-right panning)
added 6-channel rear-to-front mode