Update of Schubert's "Gretchen am Spinnrade"

Removed unused file defs.ly (no need to update it in future)
Update of Schubert's "Die Forelle"

- Slim defs.ly a bit.
- Add cross-staff arpeggios (there was some indication in the source
  that there should be such arpeggios)
Update of Schubert's "Einsamkeit"
Merge branch 'SchubertF' of https://github.com/doughdemon/The-Mutopia-Project
Header tweaks