fix problem in sedimentBottomFlux2D:
* the settling term has also to be divided by H (= bathy+eta) * the erosion term has to be divided by H instead of bath use interpolate instead of L2Projection in compute_sediment function of Tracer class
* the settling term has also to be divided by H (= bathy+eta) * the erosion term has to be divided by H instead of bath use interpolate instead of L2Projection in compute_sediment function of Tracer class