Fixed surface connection bug

-There was a bug that would cause certain triangles on the original
surface of a mesh to have no connections to the hidden surface generated
by the medial axis. Prior to this submission, the connections were
created with complex and convoluted logic. This was because the medial
axis is generated concurrently with the fracturing process and uses only
the original mesh vertices. Once fracturing finishes, none of the
fracture vertices have their closest point on the medial axis explicitly
defined. The previous logic attempted to create connects to the nearest
explicitly known position on the medial axis. This submission eliminates
this logic, however, and now calculates a fracture vertex's point on the
medial axis by interpolating the points formed by their original
triangle vertices. This ends up providing a much nicer and smooth
connection between the original surface and hidden surface.