Fill in more gaps in the matlab_block methods.

* turn matlab_block.protect_exit() into static method (and rewrite to
look nicer since heredoc style looks weird in python)
* make matlab interpreter path and options class attributes and remove
them from matlab_block.run_matlab() options.
* create matlab_block.run_matlab() but must figure out how to merge it
with bin_block.process()
* create matlab_block.process() which calls create_code, start_matlab,
and run_matlab in sucession.
matlab_block.get_parent(): fix writing of ome.tiff by the parent class.