vertical spacing: Rename properties. (issue2968042)

[markpolesky]

Reviewers: ,

Message:
Here's a patch set for this big syntax change.  I went with
"withingroup" since it got more votes.  Okay to push?

- Mark

Description:
vertical spacing: Rename properties.

Please review this at http://codereview.appspot.com/2968042/

Affected files:
  M Documentation/de/notation/spacing.itely
  M Documentation/es/learning/fundamental.itely
  M Documentation/es/notation/spacing.itely
  M Documentation/learning/fundamental.itely
  M Documentation/notation/changing-defaults.itely
  M Documentation/notation/spacing.itely
  M input/regression/page-breaking-min-distance2.ly
  D input/regression/page-spacing-loose-lines-non-affinity.ly
  A + input/regression/page-spacing-nonstaff-lines-and-markup.ly
  A + input/regression/page-spacing-nonstaff-lines-between-systems.ly
  A + input/regression/page-spacing-nonstaff-lines-between.ly
  A + input/regression/page-spacing-nonstaff-lines-bottom.ly
  A + input/regression/page-spacing-nonstaff-lines-header-padding.ly
  A + input/regression/page-spacing-nonstaff-lines-top.ly
  A input/regression/page-spacing-nonstaff-lines-unrelated.ly
  M input/regression/page-spacing-staff-group-hara-kiri.ly
  M input/regression/page-spacing-stretchability.ly
  M lily/axis-group-interface.cc
  M lily/include/axis-group-interface.hh
  M lily/page-layout-problem.cc
  M lily/staff-grouper-interface.cc
  M ly/engraver-init.ly
  M python/convertrules.py
  M scm/define-grob-properties.scm
  M scm/define-grobs.scm