Fleshing out the worker base class

Worker can now start, register, daemonize, poll for a job, and if killed cleanly, unregister.

Individual worker instances have a worker_name which must be unique to the host. This can be set in the config file or via the command line.

Stubs were added that subclasses should override to add specific worker functionality.

Tested successfully by starting the API and starting the worker by hand. Suggestions for how to automate the testing for this?