Fix bug #6930: no undo for inset type changing

Fix bug #6930: no undo for inset type changing

THis is a consequence of the new AtPoint mechanism. In the old
world, recordUndoInset was called before INSET_MODIFY. I reintroduced
manual recordUndoInset calls in all places that matter. I suspect
that this issue should be revisited later.

Note that recordUndoInset can now take an optional parameter that tells
what inset is concerned. This is useful because the cursor can be
either just inside the inset or in front of it.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@36580 a592a061-630c-0410-9148-cb99ea01b6c8