Rewrite the vertical layout of staves/systems.

[pnorcks]

I don't really understand the code from this patchset, but I just have
one quick comment.

Thanks,
Patrick


http://codereview.appspot.com/97119/diff/1/22
File lily/staff-grouper-engraver.cc (right):

http://codereview.appspot.com/97119/diff/1/22#newcode21
Line 21: {
Are engravers allowed to inherit code from other classes?

I'm asking because there is a comment in slur-engraver.cc:

   (on principle, engravers don't use inheritance for code sharing)

If the inheritance is okay, then the comment (and others, if any) should
be removed from the slur-engraver.cc.

http://codereview.appspot.com/97119