Add 'batch' option to set command

[dominikl]

Replaces closed PR #33

Adds a --batch option to the set command.

Test:
Get rendering settings from an image:

./omero -s merge-ci-devspace.openmicroscopy.org render info --style yaml Image:123 >> rend.yml

Then apply it to a whole Dataset, Project or whatever (with compatible images).

Example:

time ./omero -s merge-ci-devspace.openmicroscopy.org render set Dataset:3192 rend.yml
2.11s user 0.68s system 5% cpu 49.045 total

time ./omero -s merge-ci-devspace.openmicroscopy.org render set --batch 10 Dataset:3192 rend.yml
1.84s user 0.48s system 33% cpu 6.857 total

Needs ome/omero-py#129 to work.