Change the interface to a paragraph's layout. We still store a LayoutPtr, but now...

Change the interface to a paragraph's layout. We still store a LayoutPtr, but now privately, and make a Layout const & available to clients.

The need for a LayoutPtr arises from the fact that (a) we do not want to give our clients a Layout &, since we do not want them to be able to change our Layout; but (b) we also need to be able to change which layout is ours. So we cannot store a Layout const &. Or so it seems to the compiler.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@23522 a592a061-630c-0410-9148-cb99ea01b6c8