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.
In that case, I think the value should be just `{"database": ..., "connectionUri": ...}`

And whatever it is, it should be written up in the README for the `it` subproject.