updated model2netcdf.ED2 to generate .nc files with MsTMIP standards

changed units and dimensions.

For units, most changes required replacing "/" with negative exponents, e.g. "kg/m2" -> "kg m-2". 

For dims, I added "lat" and "lon", and changed time to "days since beginning of the year"

I also updated the tests for ncdf4, and added some checks of the variable names (this still needs work)