Issue 4275: Allow user-defined rest styles. (issue 200860043 by address@hidden)

[nine . fierce . ballads]

Reviewers: ,

Description:
Allow user-defined rest styles.
https://code.google.com/p/lilypond/issues/detail?id=4275

This is complicated by having to choose between ledgered and
unledgered glyphs based on the position of the rest on the staff,
which is not known until after line breaking.  Add the grob property
stencil-ledgered to avoid cyclic evaluation of Rest.stencil.

Hide rests in TabStaff instead of setting their stencils to #f to keep
regression tests passing after changes to rest stencil handling.

Related issues...

Failed attempt to break a cyclic evaluation of stencil in Rest_collision
instead of Rest
https://code.google.com/p/lilypond/issues/detail?id=4274
http://codereview.appspot.com/193590043

Custom stencils do not affect spacing.  I chose to create a new ticket
for this patch because the ugliness of the stencil-ledgered property
disqualifies it as a solution.
https://code.google.com/p/lilypond/issues/detail?id=4245

Please review this at https://codereview.appspot.com/200860043/

Affected files (+133, -106 lines):
  M input/regression/rest-dot-position.ly
  M input/regression/rest-note-collision.ly
  M lily/include/rest.hh
  M lily/multi-measure-rest.cc
  M lily/rest.cc
  M ly/engraver-init.ly
  M ly/property-init.ly
  M scm/define-grob-properties.scm
  M scm/define-grobs.scm
  M scm/lily.scm
  A scm/rest.scm