Implement max-systems-per-page, min-systems-per-page and systems-per-page.

Implement max-systems-per-page, min-systems-per-page and systems-per-page.

This reworks the handling of penalties in the page-breaking system.
We no longer add infinite penalties for overfilling a page; large
penalties are rather divided up into two categories: we add a large
penalty for overfilling a page and a very large penalty if we fail
to satisfy xxx-systems-per-page.

Some of the heuristics used by optimal-page-breaking have had to
be modified because they relied on the assumption that penalties
are infinite for overfilled pages.