A proposal for aligning note heads to SMUFL conventions.

It should re-enable all the note head functionality as per ver. 1.3 (and previous 2.0 releases), with most (all?) equal results.

- No new glyph added to font(s)
- Existing mscore glyphs have been matched to SMUFL note head symbols:
 - partly on similarity of shape
 - partly on similarity of semantics (in particular most of the _noteDo_..., _noteRe_..., ... heads)
- The dropped HEAD_BREVIS_ALT note head group have been re-instated (dropping it was a regression from 1.3)
- **fonts/mscore/glyphnames.json** has been updated
- **fonts/mscore/metadata.json** has NOT been updated (I have not understood its contents)


It may be improved incrementally, should the need arise.