* lily/include/paper-system.hh (class Paper_system): remove

* lily/include/paper-system.hh (class Paper_system): remove
number_ variable. Remove is_title_. Remove break_before_penalty_

* lily/paper-book.cc (systems): use 'number property iso. number_
member.

* lily/paper-system-scheme.cc: remove ly:paper-system-break-before-penalty
remove ly:paper-system-number.

* scm/lily-library.scm (paper-system-title?): new function.

* scm/page-layout.scm (ly:optimal-page-breaks): read next-space
and next-padding.
(optimal-page-breaks): rename from ly:optimal-page-breaks.

* lily/paper-system-scheme.cc (LY_DEFINE): new function.

* lily/paper-system.cc (internal_get_property): new function.

* scm/page-layout.scm (ly:optimal-page-breaks): add support for
pagetopspace

* lily/paper-system.cc (read_left_bound): new function. Read
line-break-system-details from left bound to determine extents.

* python/convertrules.py (conv): rule