[proposal] Heuristic interface to light parrallel solve call

The goal is to
- reduce the code required to make parallel search
- objectify the Strategy management, thus giving more visibility on the creation of strategies.

My proposal :
- a functional interface Heuristic, basically a Function> generating an AbstractStrategy from a Model.
- a new method in IResolutionHelper, namely Solution findOptimalParallel(IntVar objective, boolean maximize, Function modelDuplicator, Criterion stop, Heuristic... heuristics). This method creates a portfolio, iterate over the heuristics, uses the duplicator to duplicate the objective's model past first heuristic, configure this model with corresponding heuristics, then launches the search.