Improvements for Highlighting

[benory]

(1) click on a note to start the playback at a given note
(2) Implement stop button
(3) highlighting note stems

[craigsapp]

Commit bafc34d implements point 3 (highlighting note stems). Also will color notes orange when hovering on them (as part of the process of selecting a note to start playback at that point in the score):

[craigsapp]

Commit: 195ddd4

Clicking on a note while playing the music will start at that note (does not work when stopped or paused).

[benory]

(1) and (2) left to do. (3) done. If we take care of (1) then (2) is less necessary. Craig will do (1); Ben may do (2).