Add SVG treble clef from Wikimedia Commons

Source: http://commons.wikimedia.org/wiki/File:Treble_Clef_without_line.svg
Remove unneeded tags/attrs of treble clef SVG
Convert treble clef SVG to React component

And render it from the staff component, not at all positioned or scaled
properly yet.
Add `scale` prop to the `TrebleClef` component

Defaults to `1` to render at its natural size. Set to `0.5` to render at
half size. Etc.
Add spacing above staff to fully show treble clef

The treble clef was getting cut off at the top. Add spacing above
staff so that it's fully visible.
Merge branch 'treble-clef'