README.md: add a link to the ImageJ-OMERO project
POM: tidy up order of configuration blocks

This was done using:
    mvn tidy:pom
POM: add missing contributors

Both Mark Hiner and Jean-Marie Burel have commits on the project.
Add mailmap to fix Mark Hiner's email address
README.md: add "usage and benefits" section

This was adapted from the first commit message to this repository!