Add JobSet entity for better JobMonitor mgmt

[lukewendling]

Purpose

Let's revisit job running and scheduling for a more robust solution to processing historical data from QCR. We previously identified the need for a parent entity of JobMonitors, and the new entity is potentially a good candidate to drive the improved job scheduler.

Process Flow

max_retries = job interval * multiplier / loop interval

job set exists?
  N
    create
    (a) posts count > MIN_POSTS?
      N
        retry count == max_retries
          N
            increment retry counter
            exit
          Y
            set state = 'skip'
            exit
      Y
        set state = 'running'
        create monitors
  Y
    job set running?
      N
        goto (a)    
      Y
        exit