Aggregated NetCDF development

[RachaelDMueller]

• Add filepaths and number of runs to a text file with the same name as NetCDF but with _filenames.txt extension (in place of adding as variable to aggregated netcdf file b/c of technical issues with that approach)
• Create framework for looping through all the runs and creating multiple, aggregated NetCDF per oil type
• Create python script from call_aggregate_MOHID.ipynb to loop through runs and create aggregate file [working on]
• Move variable attribution information from global .attrs to [variable_name].attrs
• Add information on file creation to attribution
• Change mask attribution to remove description and include flag_meaning and flag_values. Note from Doug: See variables like tmaskutil in https://salishsea.eos.ubc.ca/erddap/info/ubcSSn2DMeshMaskV17-02/index.html as an example.
• Add full filepath and name to Filename attribute