Fixed the mesh panel, such that it displays the meshes passed into it.
Allow for the size of the spheres used for displayed verticies can be set
Added simple viewer to help debugging mesh intersection code
Added some code to validate faces.  Mainly usefull for debugging purposes.
Update boundary when removing a face, set sa_uptodate_octrees to Fasle when adding vertices
Various optional debugging features, set by class level global variables, which are likely to significantly slow down executition
Updated line_intersection_and_proportion to raise an error
if the lines do not cross and to return the propotion of the
distance the intersection is allong each line segment.
More intersection work, allowing for partial intersections of faces