The function removePicture() had a flag "last", which would indicate
that the called had finished removing pictures. Only then would
the model be recalculated.
This is a strange interface and, matter of fact, the caller was buggy:
if the last picture to be removed didn't have a proper url, removePicture()
was never called with "last" being set.
Change the interface to take a list of pictures to be deleted. This
will allow us to make picture deletion smarter in follow-up commits.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>