Added a button to the playback that toggles treble voice

[liampond]

Added optional argument treble_voice to volpiano2midi that raises the playback pitch by one octave.
Added a button, btnTreble that toggles this argument.

Resolves #827

[dchiller]

@liampond Ready to merge? If so, I can get it on staging before the meeting tomorrow.

[liampond]

@liampond Ready to merge? If so, I can get it on staging before the meeting tomorrow.

Sure, is there anything I need to do? I think it should be good.

[dchiller]

No, looks good to me! I'm happy to do it, but the general practice in the lab has been that once a PR is approved the person who opened it gets to merge it (I think in case you decide there's anything else to add?) -- anyway, just didn't want to step on your toes if there was a reason you hadn't merged.

[liampond]

No, looks good to me! I'm happy to do it, but the general practice in the lab has been that once a PR is approved the person who opened it gets to merge it (I think in case you decide there's anything else to add?) -- anyway, just didn't want to step on your toes if there was a reason you hadn't merged.

I see, makes sense. Thanks Dylan