Moves to OpenZipkin standard build process

[codefromthecrypt]

This moves a few things corresponding to recent events in Zipkin

• We no longer use Travis because it has a quota starting in New Year

  • For example, the openzipkin org is completely locked at the moment
  • Instead, we use GitHub Actions

• This uses a Maven build instead of SBT

  • It is true that SBT is less verbose, but this allows us to copy/paste
  • Notable, our deployment scripts are all set for this in all projects

• This deploys twice instead of doing cross-compile routinely

  • In zipkin-finagle, we found the easiest integration is to do this

An aside, but I also moved off some deprecated code and internal classes. I also left the "samples" directory alone, though it should probably move to https://github.com/openzipkin/brave-example

[codefromthecrypt]

tested and works!