add barotropic alternative: interpolate uv3D.th.nc from hycom

[water-e]

The barotropic-baroclinic sequence is probably the least intuitive step in our workflow. It would be nice to see how coastal velocities work as a substitute.

uv3D.th.nc can probably be taken from hycom for the period where it is available, which means situations that follow from hindcasts with relatively little large scale change (landscape, sea level).

We should also probably generalize the idea so that we can take it from the West Coast Forecasting System, although currently this is relatively new and just on the to-do list.

Zhengui from VIMS has a one-off script to do this.

We would separate download and put an I/O systme on this to "BayDeltaSCHISMify" the script. Can we do this and test it?

https://github.com/wzhengui/pylibs/blob/master/pyScripts/gen_hycom_3Dth_nudge.py