Fix memory leak in KoShapeContainer.

This fixes a big memoryleak resulting in quite a lot of shapes not getting
deleted when the document is deleted.

This also fixes crashes on shutdown currently seen in cstester in quite some
calligra words files.
Problem for the crashes is that some shapes and QTextDocuments while others
still trigger relayouting which uses the no longer deleted objects.

The patch fixes that by deleting the shapes and making sure there is no
relayout when the stuff is deleted.

Thanks for boud and boemann for the review. The problem boemann pointed out
has been fixed.

REVIEW: 108937