POM: simplify repositories blocks
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.
POM: update repository URL where appropriate
POM: remove no-longer-needed configuration blocks

The removed sections have all migrated to the pom-scijava parent.
POM: use new bsd_2 license, not custom resolver

The license-maven-plugin 1.6 adds BSD-style license templates:
  https://jira.codehaus.org/browse/MLICENSE-80

With this fabulous new addition, we can eliminate our custom
license resolver in favor of the stock bsd_2 license.
Update license and file headers

This was done using:
  mvn license:update-project-license license:update-file-header

The only real change is the loss of the legal disclaimer at the bottom
of the license. This disclaimer is not actually part of the BSD-2
license proper, but rather an addendum. For relevant discussion, see:
  https://jira.codehaus.org/browse/MLICENSE-80