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.
Yes, the backend name as specified in the test is mapped to `SLAMDATA_<name>` (where `<name>` is the name of the backend), and that environment variable checked for an override setting to the default. Will definitely document this in the it README.