add support to find multipolygon inside polygon or multipolygon with ContainsFinder
add some unit tests
performance_1: improve isPolygonInsideMultiPolygon() by using the areas calculated
in MultipolygonBuilder.joinWays() instead of calling getArea() again.
performance_2: improve isPolygonInsideMultiPolygon() by first checking bounding boxes (helps with complex MP containing many inners as it avoids the Area.intersect() method)
performance_3: implement new methods to reuse result of complex method MultipolygonBuilder.joinWays() in ContainsFinder