Add worker to qless-java binding

The original implementation of qless-java binding does not provide "worker" concept like what have been done in its python/ruby binding. Inspired by [qless-py] (https://github.com/seomoz/qless-py), we implemented a simple serial worker to allow us for further Meerkat integration. Note this is a minimal implementation of [SerialWorker] (https://github.com/seomoz/qless-py/blob/master/qless/workers/serial.py) in qless-py. We still miss several advanced features like "signal", "resume" and etc.
The original repo does not apply "final" for all temp variables and that's why I turn off the "final" check in Eclipse - otherwise that will introduce a lot of changes. I can add "final" for the parts I owned but that will make code inconsistent.