Analytical_Engine: Improve performance of creation of large graphs with DomainTree

#### Description:
Creating graphs using the method that takes a collection of curves and a collection of entities currently requires searching all the provided entities to find the closest to each end point of each connecting curves.

At present this is done crudely and OK for up to 1000 entities. Beyond this processing times become very slow. Proposing here that the search approach is refactored possibly leveraging the DomainTree.

This issue arises from prototyping the creation of a circulation graph for a sports venue where entity frequently counts exceed 10000.