Blitz param types 11637 develop

Fixes a couple of errors where Blitz gateway doesn't enforce the correct parameter types, noticed on howe. See https://trac.openmicroscopy.org.uk/ome/ticket/11637

To test, this should work without throwing exceptions:

ssh to gretzky...

$ cd lib/python/
$ python
>>> from omero.gateway import BlitzGateway
>>> conn = BlitzGateway("username", "password", host="localhost")
>>> conn.connect()
>>> image = conn.getObject("Image", <imageId>)
>>> image.setActiveChannels([1], [[10,100]])                # previously this threw an exception
>>> image.renderJpegRegion(0, 0, 0.1, 1.0, 10.1, 10)  # previously this threw an exception
Not entirely sure why these methods never failed for me on my local machine.

--rebased-from #1700