Slashed Half-flat and add. scales for Arabic music

Slashed Half-flat and add. scales for Arabic music

-Introduced a glyph list so that the slashed half-flat is used
(always) instead of the mirrored one (the latter is never used
for Arabic sheet music)
-Added two scales (Maqamat) of major importance for Arabic music

For arabic music score writing:
-Introduced new glyph list, so that by default the slashed
half-flat is used instead of the mirrored half-flat, which isn't
used in Arabic score writing. This makes the use of the cumbersome
\dwn symbol needless and obsolete
-Added Hijaz and Hijaz-Kar maqamat