[Master/Worker] Implement the concrete worker context concept

[Jack12816]

The first dependency for this feature is the ability to
build a default CLI for the worker and master implementation.
This should be done with node-getopt, like in the greppy binary.

A good starting point would be a worker switch which names
the concrete worker implementation for both worker and master
scripts.

Concrete worker implementations name the modules to load
and further details for the worker context.

This enhancement is a dependency for file-based logging
out of the box and for proper cluster-slave statistics.

[Jack12816]

Done with 924e301.