PMMC09 and vertical resolution

[SebastienRietteMTO]

When vertical resolution increases near the surface, the scheme closure happens too near the surface and can lead to an overestimated transport.
The idea of Valery is to modify the closure mechanism to take into account the environment variables values higher and start the updraft at a given height above ground (maybe around 20m). The difficulty is to impose updraft characteristics under this point to allow the mixing on the whole column and not only starting from the 20m level.

[SebastienRietteMTO]

Modifications done by B. Viala must be merged