This commit adds a Stochastic Kinetic Energy Backscatter Scheme (SKEBS)
where the amplitude of the backscatter is based on either the GM
work rate and/or the viscous work rate (FrictWork). Each of these
can be multiplied by a coefficient so that, e.g. the backscatter rate
could be 50% of the GM work rate plus 20% of the viscous work rate.
The vertical structure of the backscatter rate associated with GM has
vertical structure given by the EBT profile. This code was developed
starting from Phil Pegion's branch, and it builds on the stochastic
physics package (external) developed by Phil Pegion, Niraj Agarwal,
and collaborators. This package allows the length and time scales
of the backscatter to be set via namelist parameters. This commit
may break the stochastic EPBL and SPPT schemes developed by P.
Pegion.