Implement Anchor Processor

[AgeManning]

The processor is a task that sits between the network and various client components.

As tasks can process items at different speeds, messages need to be prioritized over others and dropped in some cases to prevent backlogs of work.

Furthermore, grouping all the heavy lifting blocking tasks (i.e signature verification) can be localized into logical task to optimize the bulk of the processing of the client.

The processor schedules, queues and prioritizes work elements for the Anchor client. See the Architecture overview in the book for further high-level information.

A similar concept is the beacon processor in Lighthouse.