Add metadata on riksdagsår

[MansMeg]

Now when Lotta is looking up Riksdagsår, we should add the following information to the riksdagsår metadata file:

• [ ] Split up between chamber (since we have different dates, I think this will be done)
• [ ] Add a column with source/reference that we can use both to update wikidata and to help other projects to assess the quality of the datapoints