Implement ThreadedWorkerPool

[Framstag]

The header Worker.h defines a ThreadedWorker and some derived classes. Sometimes will want t process a queue by multiple instances of a ThreadedWorker (a pool).

In this case we would like to have a template of a specific Worker class, with the following features:

• allows to construct a number of worker instances with the constructor arguments passed to the pool template
• start the worker
• expose a Wait() methods, that allows to wait for all worker to be finished
• Frees all workers

See GenMergeAreas.cpp, MergeAreas for a manually crafted example