Ottava Clefs (try 2)

8va Treble clefs added. See Request #236 for background -- There are still about 7 too-many commits here, but the net result is 4 files changed in a manner that should be easier to see. 
Nitpick: No need for temporary `clef_obj`.
```
this.clef = (new Vex.Flow.Clef(clef, size, annotation)).clef;
```