Support PlanarImgs in the ArithmeticOps

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Refactor the unit test for the Javassist meta op

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Test the support for PlanarImgs

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