Surface related checks and methods

Geodesic distance:

• TODO: Probably should check that max_dist isn't "too" large or too small, min should probably be max edge length...
• Based on the descriptive statistics (edge histogram), give a sensible value for the maximum cutoff distance.
• TODO: Probably should check that targets and start_vertex are less than thw number of vertices, etc...
• Check that that source and target vertex indices are within the surface dimensions.