Pull source data from EASIN API

[peterdesmet]

See https://easin.jrc.ec.europa.eu/api/cat/euconcern/

[damianooldoni]

Done in branch fetch-from-easin-api.
Although the data fetched via EASIN API are very good in listing all synonyms (sometimes we have 7!) and providing a lot of other kinds of information such as introductions, common names (not only in English!), species pfoiles and pathways, it seems however that the list of accepted taxa is not complete: we have only 48 accepted taxa 😢

I think this should be solved if we want to publish the checklist on GBIF based on data harvested by EASIN API.

[damianooldoni]

We stop at the moment the work about harvesting raw data via EASIN API due to missing information, see #9.
Branch fetch-from-easin-api will remain of course.