REP-1283 DeRP Filter

I'm not sure if system level tests will be necessary for this story? Since I can actually test the Java filter API doFilter method, my unit tests are fairly comprehensive and can be expanded to cover more cases. Actually, I suppose we need a test for the response messaging service, at least.

Note: The tests won't pass on this branch until we cut a release of http-delegation. We should also probably update the version api-checker uses.
It does get processed through the response messaging service. That happens in the PowerFilter class. It seems like it shouldn't process what sendError sends since sendError should commit the output stream, but I wrote a test that passes, so...