Cleaned up in the DSC thresholds.
Added a function which checks that an edge e can be removed by the topological edge removal operation.

Currently checks the flatness of the interface by calculating the
dihedral angle, but could use volume instead.
Split the topological pass function into two (topological edge removal and topological face removal).
Updated the functions which calculates the dihedral angles.
Moved calculation of the dihedral angle to utility.