Edited MAX_THREADS to confirm correctness over multiple CUDA blocks
copied simulator for heateq and removed the implicit solver. Still need support for centroid to compile
Implemented Centroid(CollOfCell)
Changed centroid(CollOfCell) to centroid(CollOfIndices).
Added member variable face_centroids_ to DeviceGrid.
Implemented Scalar/CollOfScalar
Implemented copy assignment operator for CollOfScalar. Needed for datatype Mutual Collection Of Scalar
exp_heateq.equelle now compiles with two backends which produce same result!