* Move sound_init to make sure it gets called everytime user
preferences is reloaded.
* Merged sound_reinit and sound_init. One used user preferences
while the other did not, don't see the point of this, so just
made it always use user preferences now.
* Timeline header audio sync option now controls scene flag
rather than timeline flag. Since it uses the same playback
operator now, there is no distinction anymore.
* Added boolean property sync to animation play operator, to sync
with audio or not. Uses scene setting if property is not set.
* Playback stop button in info header now calls operator, so sounds
stop playing too.