Make the AddOp a bit more generic

It can process *all* the ArrayImgs now, thanks to classes generated on the
fly using Javassist. Ah, Javassist. You're so cool.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Verify in a unit test that the code generation works

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>