Changes

Add release notes for OMERO.server 5.6.16

See
- https://github.com/ome/omero-gateway-java/releases/tag/v5.10.3
- https://github.com/ome/omero-blitz/releases/tag/v5.8.3
- https://github.com/ome/omero-server/releases/tag/v5.7.3
- https://github.com/ome/omero-renderer/releases/tag/v5.6.3
- https://github.com/ome/omero-romio/releases/tag/v5.8.3
- https://github.com/ome/omero-common/releases/tag/v5.7.3
- https://github.com/ome/omero-model/releases/tag/v5.7.3
- https://github.com/ome/omero-scripts/releases/tag/v5.9.1
- https://github.com/ome/omero-py/releases/tag/v5.21.0
- https://github.com/ome/omero-web/releases/tag/v5.29.1