Manager must persist in-memory data structures to disk

[modeswitch]

The manager keeps track of some state (device types, jobs, etc) that should be written to disk periodically and loaded when the manager starts.

[jmaher]

For every transaction that we have, we can abstract each call from client/worker to a given json file.

[jmaher]

todo: define what all the state parameters are

[modeswitch]

The most important things are:

• worker device types (so we don't have to remap them on restart)
• active jobs and their states

I wouldn't worry about active tasks. If the system is restarted with active workers, those results can just be discarded and the tasks will be restarted.