Parallel Computer

This is an implementation of PC moved from my private repo to surefire project.  It will fix and improve the PC.
This impl can distinguish between JUnit classes (tests) and suites, so it will introduce more options in the element `parallel`:
+ classes
+ suites
+ methods
+ classesAndSuites
+ suitesAndMethods
+ classesAndMethods
+ all (same behavior as old both)
 
Additionally, we can have new params in plugin's config for the specified number of Threads imposed on:
+ suites
+ classes
+ methods
 
among of the existing configuration param for the total number of Threads.

Additionally the Threads can be shared or not shared between these categories. We should think about the names for the new configuration parameters.