switched to thread pool server

These changes switch from the simpleserver to the threadpoolserver (@dmnapolitano did that part), makes some tweaks to the readme, and adds a default log4j.properties file to avoid warnings when running the server.

note: We've found the threadpool simpleserver thing to be kinda flaky, so we moved to the thread pool server in our other projects (e.g., https://github.com/EducationalTestingService/stanford-thrift).