Makes LFO sync with the timeline of the song

Fixes https://github.com/LMMS/lmms/issues/204

Warning: This breaks backward compatibility because in previous versions:
* LFO-controlled knobs were not synced with the time of the song.
* The phase offset of LFO was bugged.

EDIT: Please notice that the damage is pretty low because only the compatibility of phase offset is broken.