Caches the interior skylines of vertical axis groups and systems. (issue 7185044)

[k-ohara5a5a]

This would take me a couple more hours to figure out.  Do I want to ?

It seems the "caching" is not the type that saves us from
re-computation.  It simply stores the skylines Scheme objects.

The tracker says the overall goal is to remove a call to the function
translate_axis.  In the example
 { g4\> g'_"pico"  g' g\! }
when we decide to move the "pico" between hairpin and staff, the call to
translate_axis records the new position in the TextScript grob itself.

Sometime before printing, I assume you want the positioning information
to be updated in the grob.  When do you propose to do so ?   How will
storing the outline of the staff without the hairpin in
'inside-staff-skylines' help ?

You can post a commit series to Reitveld if you like.  On the branch
with the final commit, just checkout the first commit, `git-cl upload
master`, checkout the next commit...


https://codereview.appspot.com/7185044/diff/4001/scm/define-grob-properties.scm
File scm/define-grob-properties.scm (right):

https://codereview.appspot.com/7185044/diff/4001/scm/define-grob-properties.scm#newcode1115
scm/define-grob-properties.scm:1115: grobs that are elements of an axis
group that do not have an
"elements of a @code{VerticalAxisGroup} and that do not"

https://codereview.appspot.com/7185044/diff/4001/scm/define-grob-properties.scm#newcode1117
scm/define-grob-properties.scm:1117: or other vertical axis like lyrics,
dynamics, etc..")
"or other @code{VerticalAxisGroup}s like @code{Lyrics}, @code{Dynamics}"
because dynamics like \p \< \f typically do have outside-staff-priority.

https://codereview.appspot.com/7185044/