Remove redundant/unused workstates

As discussed here:
https://groups.google.com/a/pyfarm.net/forum/#!msg/discuss/Qd7zAdSDTMc/NiacNdKwAbwJ
Fake queued, running, assigned states in job api
Merge pull request #122 from guidow/reduce_workstates

Reduce workstates
Experimental scheduler as asynch. celery task
Cosmetic change: stay within 80 cols
Simplify getting requirements_to_satisfy
Simplify return statement
Don't use an empty list as default parameter
Simplify getting num_tasks_by_prio
Use AgentState, WorkState instead of strings
Always use generator type range()
Use positional parameters for logging
Rename q -> query, prio -> priority
Rename celery module to celery_app
Include pyfarm's logger instead of celery's
Add TODO notice about logging configuration
Simplify creating job_query
Use representation in log string
Added a short README with hints for running celery
Honor job dependencies

Jobs with any dependencies that are not "done" must not be started.