Add treble_8va and treble_8vb Clefs

Added an ottava object to new treble_8va and treble_8vb clefs which are added as a second, zero-width glyph to denote music that sounds an octave higher than written (piccolo music) or an octave lower (some guitar transcriptions).  Added tests to clef_tests.js.  What doesn't work and I'll need some help with, is the clef change, since I am unclear about how to add two glyphs via a clefnote object. If anyone can help with that I'll work out the metrics for the other common 8vas (essentially just, bass_8vb; I don't know of any usage of another).

(also added .project to gitignore -- generated automatically by Eclipse; hope no one minds).

First Vex.Flow pull request, so please feel free to tell me what I should NOT be doing, so that I can do better in the future. Still new enough on Javascript that I want to get things right.