Facederivatives

Fixing face derivative calculations for collapsed elements. The previous face calculations only worked for tricubic-Hermite elements. Some examples, e.g. linear Lagrange-bicubic Hermite, will change as things are now done correctly. Fixed exporting of sector elements. The code no longer crashes but it still doesn't produce .ex files that can be read into cmgui. 
I noticed there's a `LOGICAL :: HERMITE` member in `BASIS_TYPE` that isn't actually used except to be initialised to False and should probably be deleted.