Update mailmap
POM: tweak org name

We aren't actively using "ImageJDev.org" anymore. It was awkward.
POM: update developers and contributors

According to the Maven docs, the "developers" section is supposed to be
for active developers. Rule of thumb: people you would contact with
questions about the project. The "contributors" section is for people
who contribute(d) to the project, but who are not officially responsible
for it. So a few of the people formerly tagged as "developers" are more
properly listed under "contributors" instead.

Wayne Rasband and Lee Kamentsky are borderline (Wayne deserves no blame
for any crappiness in the ImageJ2 code!), but I think an argument can be
made for each to still be listed as a "developer" rather than a
"contributor" at this time.
POM: remove no-longer-needed configuration blocks

The removed sections have all migrated to the pom-scijava parent.