The most important change in this changeset is that InsetCollapsable::getLayout

The most important change in this changeset is that InsetCollapsable::getLayout
is commented out, so that the documentclass is queried every time instead of
using the layout_ cache. For now I have kept the setLayout calls, but they are
inoperant.

Other changes:
 * remove non-const usePlainLayout methods
 * move InsetCollapsable::allowSpellCheck and allowMultiPar to InsetText
 * move InsetCollapsable::isFreespacing and forceLTR to Inset

Freespacing support could be moved to insettext, but I have to check who
uses it.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@30549 a592a061-630c-0410-9148-cb99ea01b6c8