MVP for dedicated Workers project

[jvyden]

Partially addresses #786.

This has a number of changes that will be required for making Refresh more scalable, as well as generalizing the implementation to support jobs that have unique lifetimes (e.g. those who do not need to repeat constantly, or run every tick, or only once on startup).

• IWorker is now WorkerJob. Henceforth "Worker" will refer to the process running these "Job"s.
• The base classes required for workers to function have been separated to their own project.
  • WorkerJob is now in Refresh.Workers
  • Jobs like ExpiringObjectJob stay in the interface project.
• Jobs have been refactored to be able to specify their own conditions for being able to run. For example, we now have RepeatingJob which is the old behavior. I've introduced StartupJob as well, or you can use the default WorkerJob which runs every tick by default.
• Information and metadata regarding Worker status is now in the database. This stores when the worker was brought up, when the last cycle was run, and it's class. The class specifies which codebase the worker belongs to (e.g. we will have a worker implementation for both Refresh and Toolkit) - and only one worker of a class can exist at a given time, new ones that start up will cause the other worker to shut down.
• A very very barebones executable Refresh.WorkerManager project was introduced. This simply runs a WorkerManager, but lacks any ability to configure it. I will complete this in a follow-up PR.