#111 Notes layer real time MIDI output

[Craig Stuart Sapp]

In Notes layers, the notes are currently being
played internal to SV (I am not complaining :-).

However, now that you have MIDI input, it would
be nice to also allow users to select where the play-
back of the Notes Layer is being realized.
There could be a selection on the Notes Layer
control window where the different outputs
(internally, or via a MIDI output stream) could
be selected.

In addition, it might be nice to have a control
for the user to select which MIDI channel the
notes will be played on.