local models

[rmojgani]

@jakharkaran
I have made a branch to work on local models , starting with local Leith. here is the $\Pi$ and their difference

$$\Pi = ∇.(ν_e ∇ω )$$

versus

$$\Pi= ν_e ∇.( ∇ω ) == ν_e (∇^2ω )$$

Can you review the implementation ?

py2d/py2d/SGSModel.py

Line 38 in 80d1db6

elif method == 'DLEITH_Local':