Wrap Runnable in custom Job Runner class

[KenSuenobu]

Instead of submitting a job via a Runnable interface to JobExecutor inside the Job class, it should be more intelligently wrapped in a JobRunner class. This way, the job can have some direct control over how it's run.

Potentially, we will have the ability to stop/cancel a job, and run an "onFinished" method that gets called depending on the status that occurs after a job finishes.

Just implement the "onFinished" method for this code. Other methods will come as they are developed.

[KenSuenobu]

Implementing "onFinished" for the time being. There's no way to currently check for exceptions or cancelations (yet). These will be included in new tickets.