Enforce licenses

[akomakom]

• core never enforced header licenses due to a pom error. Using new parent that enforces licenses.
• All headers have been brought in sync using mvn license:format
• Due to a change in license plugin configuration, a trailing blank line is removed from all files.
• parent also adds spotbugs execution

[akomakom]

@myronkscott I have these options:

1. Disable spotbugs for now and deal with fixing violations in a separate PR
2. Fix them in this PR

The downside of option 2 is that the diff is already overwhelming. But it's fine with me.

[myronkscott]

Disable spot bugs for this repo. Too much legacy to deal with. I don’t think it is worth it.