Preliminary data validation

[energyLS]

See pypsa-meets-earth/pypsa-earth#587 for details

[davide-f]

The starter kits by osemosys could be good for some country-scale validation too: http://www.osemosys.org/starter-kits.html

[davide-f]

Very nice draft :D It is moving good!
As a comment, I think also the continent column could be cool to add as it may enable simple automatic plotting that may be highly useful.
To do so, I'd recomment country_converter (we rely on it); see here on how to use it, super easy to do