Euclidean generator and tsp enhancements

[megyhazy]

Thoughts:

• Generates complete graph. Does this need to be in the prototype name?
• There is an example that prints graphs and executes an MST algorithm. Maybe unecessarily complex and can be removed.
• This is the beginning of refactoring the TSP heuristics to be more modular and have re-usable components vs the way it is now. I intend to refactor metric_tsp and then add nearest_neighbor
• This is related to issue Euclidian Random Graphs Utilities #452