12373 grid config

I recently asked @kennethgillen to take a glance at the properties in `etc/omero.properties` for readability etc. This PR is probably as good a place as any for suggestions for improvement. This may also go along with the recent discussion under https://github.com/openmicroscopy/ome-documentation/pull/826

 * [12373](https://trac.openmicroscopy.org.uk/ome/ticket/12373) - fix urls
Is  ae4bae5 clearer? :smile: