Add jrc data

[joseph-palmer]

This PR adds a national class for country and regional data from the European Commission's Joint Research Centre (JRC).

Data source: https://github.com/ec-jrc/COVID-19

country codes are provided but region codes are not. I think it would make sense, if possible to find a repo or something containing region code data which we can link to all classes. This way we could do away with having to define region codes in the actual classes themselves. Whilst this to much of an issue for specific countries, for these national sources unless they are provided its difficult to get them...

closes #232

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