Changes

This commit switches the names, but not the values, of the dp1 and pr1 variables for up2 and vp2.  In other words, up2_dp1 <---> up2_pr1 and vp2_dp1 <---> vp2_pr1.  This makes the terms in these equations more consistent with the terms in the wp2 equation.  I believe this commit is BIT_CHANGING since it will affect the values of these variables even though the nightly plot profiles should not change (but the budget plots would have these lines swapped).

Sensitivity matrix code now reads netcdf files by default.
Also puts observations into a function,
adds doc strings, and fixes indenting.

For #910.

Create new driver function, analyzeSensMatrix.
Now the only code left in main() just prescribes
input values and calls analyzeSensMatrix.
Unfortunately, this version does not work with
netcdf files from E3SM, which are newer than
what scipy can handle.  I'll probably
need to upgrade to netcdf4.

For #910.

Change netcdf package to netCDF4.  Now Zhun's
netcdf test files in #910 can be read.

Observations value for global mean and regional mean.