Use ome.staging for Maven release deployment (rebased onto dev_5_0)


This is the same as gh-1329 but rebased onto dev_5_0.

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This should allow the http://ci.openmicroscopy.org/job/BIOFORMATS-5.1-latest-maven/ job to deploy release versions to ome.staging instead of ome.releases on our artifactory. Promotion of Maven artifacts to ome.releases should follow release acceptance (like the OMERO jobs)