Misc header fixes

This includes several utf8 encodings:
BachJS/BWV1010/bwv1010/bwv1010-lys/bwv1010-cello.ly
BachJS/BWV1010/bwv1010/bwv1010-lys/bwv1010-viola.ly
BachJS/BWV1010/bwv1010/bwv1010-lys/bwv1010_bourree_ii.ly
MozartWA/KV421/k421/k421-lys/defs.ly
MozartWA/KV626/dies_irae/dies_irae-lys/score.ly

... a header in two parts that was merged into a single header:
BanksJK/opsinist/opsinist.ly

... a footer added:
CouperinF/ArtDeToucherLeClavecin/ArtDeToucherLeClavecin-lys/mutopia-header.ly

... and footer's corrected (as mutopiafooter):
PergolesiGB/glorytogod/glorytogod.ly
SzervacA/Ostia/Ostia.ly
SzervacA/REMIX_AE_I/REMIX_AE_I.ly
SzervacA/Tritto/Tritto.ly