Need to specify data type for DG0 solutions. Otherwise dealii complains that it does not know data type.
Updated positivity limiter from Pablos changes; use right_hand_side and copy result into current_solution at the end. Commented out some steps on predictor since we dont need it for explicit RK.
Remove Pk and mood option from src_gll. compute_cell_average is made more efficient.
merge changes manually