Added new function islandora_copy_object() can copy existing/new fedora objects.

It's a bit leaky in that it makes assumptions about the members that will exist
on AbstractObjects, but we can't make cloning work at the moment as it doesn't
really work well with inheritance, every decendent would have to define __clone
functions properly and I figured a wrapper function like this would be easier
to support in the long term, until we make the movement to decorated objects.