First steps towards an auxiliary semi-Lagrangian (i.e. split advection) scheme for momentum.
First steps towards an auxiliary semi-Lagrangian (i.e. split
advection) scheme for momentum.

Added an optional subcycle_m to the interface to Momentum_DG which
contains the advection and Coriolis terms, these are correspondingly
not added into big_m.


FluidityProject/multifluids,FluidityProject/multifluids,FluidityProject/multifluids,FluidityProject/multifluids