Add support for anytime algorithms

[gonzalezsieira]

Some basic classes need support for anytime algorithms like ARA*, Weighted A*, etc.

• ProblemBuilder needs to take as input the scaling factor of the heuristic and the scaling operation when dealing with generic costs.
• Same applies to GraphSearchProblem, which is the easiest way to create graph search problems, like those in the examples.
• SearchProblem needs an extension to deal with these parameters.