Add habitat

[peterdesmet]

Provided in https://easin.jrc.ec.europa.eu/api/cat/euconcern/ (terrestrial, freshwater, etc.)

[damianooldoni]

Actually mapped in branch https://github.com/riparias/union-list/tree/fetch-from-easin-api.
However, such way to retrieve raw data is on hold until #9 is solved.