Mappings should emit statements with lineage data

[pudo]

We now have the statements data model available, and mappings have some extra info that may be interesting to retain such as:

• original_value from CSV or SQL columns prior to their normalisation.
• Put CSV file names and row numbers, as well as SQL column references in origin
• Allow mappings to specify a lang

Mappings aren't used by OpenSanctions, so I'm also marking this good first issue for community contributions.

[KDivyasri]

Hi, I'd like to try the issue!

[pudo]

Brilliant! I think a good way to go about it would be to see if you can understand the code path for a simple CSV mapper. Then maybe switch the entity type it generates to statements, and try introducing original_value to the prop .add() calls. Finally, minting origin values based on the source name and location (eg. politicians.csv:1837).