Relicense to Apache v2

- Add LICENSE and NOTICE files for both the repo and the tar/zip/rpm
  that can be generated
- Add the Apache v2 license header where appropriate (some Scala library,
  Passera, and Open Grid Forum files maintain their existing permissive
  licensing)
- Update tests that had line number changes due to the new license header
- Add .rat-excludes file for use with Apache Rat so that it ignores test
  files and files we expect to not have a non-Apache license
- Remove sbt license generator plugin. It cannot generate the type of
  license file we want and adds extra sbt complexity for licenses it
  does not know about or packages for which it can't automatically
  determine the license. Easier to just manually maintain license files.

DAFFODIL-1859