Delete rois docs

[will-moore]

This improves our documentation & examples of deleting ROIs with conn.deleteObjects() and gives an example of using the wait=True parameter.

See http://lists.openmicroscopy.org.uk/pipermail/ome-users/2016-January/005822.html

Check that tests are passing for these examples and the code changes & comments make sense.

[joshmoore]

One other option here that I've used recently when testing your and my example PRs is:

bin/omero delete /Image/Roi:$IMAGEID

[will-moore]

@joshmoore That's useful for sure, but should probably go under CLI docs rather than here.

[ximenesuk]

This looks good to merge unless @joshmoore has a strong reason for a skiphead delet being used.

[joshmoore]

Yeah, I'll merge since adding another example would require a code change, but I was thinking less of that for the CLI docs, but that such an example would also be useful for the gateway.