Redid horns, added manual barring, cosmetic changes in source, added rehearsal marks to parts

Changed horns to use individual parts and partcombine instead of chords,
in case someone wants to print separate parts later. Added barring to
keep r8 a r a together, as in original parts, and similar situations.
Added rehearsalMarks to all parts and score. Changed combined parts to
not print a2 etc.