Refactor Task Manager out of client

The Task Manager is currently used in the client because there is some useful code there that could be used from the client (sending messages, listing jobs, setting up pubsub clients, etc). This should really be refactored out to stay just a core piece of the server. We could possibly just refactor it into a TaskManager{Base,Client,Server} to be more explicit what should be used where, and also to only load what services we need in either case.