Abstraction for parallel computer

We agreed that multiple files is needed for new parallel computer.

After #523 i understood how the structure should be like:

+ Scheduling Strategy. An abstract class with factories which can run tasks in a sequence or in parallel, or parallel-sharing own thread pool with other strategies;
+ Abstract Executor. Controls the strategies, balance the amounth of shared threads in a strategy, blocks and shuts down, and awaits the strategies to finish;
+ Computer and builder

In the first commit are the strategies.
I will try to submit next two every next day.