Update conversion of ECCC flat files and new Climate Summary files to CF-like NetCDF

[Zeitsperre]

The ECCC climate summary files have changed their format to something more machine-readable in the past year or so. This renders the old code that parsed the metadata fields that were prepended in CSV files obsolete.

We can remove a good chunk of this handling to read data directly into Pandas dataframes, output to NetCDF, then run them through the conversion process with the proper JSON definitions.

For better management of flat file conversion, we need to convert the existing ECCC dictionaries to JSON definitions. Unit conversions should be performed exclusively through pint.