Merge pull request #228 from joshmoore/rebased/develop/contrib-section

"Contributing to OMERO" developer doc rework (rebased onto develop)
Add extlink alias to create links to the right OMERO-*-virtual job
Fix virtual appliance link using newly defined extlink
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 232 (Remove extra spaces on build system links.)
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 233 (Virtualjob extlink (rebased onto develop))
merge develop -D org -I include -E conflict -E needs-fixes -E broken

Repository: openmicroscopy/ome-documentation
Updating dd7e4e5..0376ea2
Merged PRs:
  # PR 232 mtbc 'Remove extra spaces on build system links.'
  # PR 233 sbesson 'Virtualjob extlink (rebased onto develop)'

Generated by OMERO-merge-develop#130 (http://hudson.openmicroscopy.org.uk/job/OMERO-merge-develop/130/)