Feature/livenotes

This PR adds the ability to distinguish *live* vs *banked* notes on the sheet music. Banked notes should now appears as quarter notes without stems, and live notes should appear as whole notes.

This PR also fixes an issue with live notes where they were disappearing (i.e. cleared) when a bank occurred. This wasn't the desired behavior. As long as the chord is being played and the keys are down, they should appear in the *live* chord.

@jazahn or @MichaelDHilborn-Harvard  Can you take a look at this when you get a chance?