* Remove Node from data model; standardize on Worker
This commit does a lot of things, but in general it attempts to simplify
the data model by getting rid of the Node and NodeRole models. Instead,
these will use the Worker model, which itself has individual boolean
fields for role types.
Get rid of roleType in some FreeWorker methods
rename NodeService to WorkerRegistry
simplify the freeworker interface
fix the tests
* Remove DeleteWorker method from workerJobService
