Consider dropping CBS ids

[joepio]

We currently map every municipality to CBS and Allmanak identifiers. If I remember correctly, we did this because we pulled some data from these sources, like the logo of the organization.

Since we now pretty much exclusively focus on the Documents instead of other resources, I'm not quite sure if we're still using these mappings.

It would make the codebase and the sourcefiles a lot cleaner if we can deprecate these. It would also speed up the process of adding new municipalities.

[joepio]

According to @robvandijk the allmanak is still used, but the CBS id doesn't seem to be.