improve build process, part of #481

fix oneJar code coverage issue (coverage info corrupts JAR), test built SlamEngine JAR, allow environment variable overrides of backend-config, modify travis to use local mongodb override, auto-import zips data set when in travis builds. note: publish script has not been updated and jenkins is no longer expected to work.
Wait, is the key encoding the backend type? Maybe that's what I'm missing here. In that case, it's a bit confusing, but I rescind my objection.