mscore font: add glyphs corresponding to SMUFL clef-number glyphs

The mscore font is lacking some of the glyphs in the SMUFL set. Clef+numbers glyphs are required to simplify SMUFL integration.

Code points:

G clef 15 above: 0xe1d6
G clef 8 above: 0xe1d7
G clef 8 below: 0xe1d8
G clef 15 below: 0xe1d9
F clef 15 above: 0xe1da
F clef 8 above: 0xe1db
F clef 8 below: 0xe1dc
F clef 15 below: 0xe1dd

Metrics: same metrics as the clef alone glyphs.

Also:
- added references to some glyphs used in Renaissance editions at SMUFL code points too (original points still valid);
- cleaned the most serious warnings about the font (intersecting paths, wrong path directions). A full clean-up will take quite some time, given the large number of paths missing extrema (milder warning);
- generated TTF font in addition to OTF.