At least JPEG files are now only loaded when the user scrolls to the
relevant page.

Also fix the root cause of the EMF lazy-read problem and remove the
previous workarounds.

Change-Id: I9699927282b99bcb71a0d271a20bbfd56a361ee8
Reviewed-on: https://gerrit.libreoffice.org/53219Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>