Allow predefined diagrams regardless of note names language. (issue2791041)

[v . villenave]

Reviewers: ,

Message:
Hi everybody,

here's a patch that should allow users to stop worrying about whether to
include fretboard diagrams before or after choosing the note names
language.

I've updated the docs accordingly; hopefully there are no other .ly
optional init files that rely on hardcoded note names (bagpipe.ly is
basically a language file of its own).  Please let me know if there are
other caveats I overlooked.

Cheers!
Valentin.

Description:
Allow predefined diagrams regardless of note names language.

This should make the @warning in NR 1.1.1 "note names" no
longer needed.

Please review this at http://codereview.appspot.com/2791041/

Affected files:
  M Documentation/de/notation/pitches.itely
  M Documentation/es/notation/pitches.itely
  M Documentation/fr/notation/pitches.itely
  M Documentation/notation/pitches.itely
  M ly/declarations-init.ly
  M ly/language-init.ly
  M ly/predefined-guitar-fretboards.ly
  M ly/predefined-ukulele-fretboards.ly