Add new fns use_debug and with_debug:

use_debug false # turns off all trigger messages

with_debug false do
  # turns off trigger messages within this block
end

* Allows synth and sample triggering messages to be silenced/allowed on 
  a per thread basis
Use more idiomatic foo= method for setting sched_ahead_time:

* add both getter and setter methods for sched_ahead_time in studio
Remove debug statement
Fix bug in studio@sched_ahead_time - shouldn't require a param
Delay messages by sched_ahead_time to keep messages in sync with synths