Group projects by revision chamber ID

[martinszy]

Some projects have gone to the revision chamber and are assigned a different ID there. I think we may be duplicating those projects when they are actually just one. Please check it.
In case we are, I think we should make something like a "bill group" that could contain several expedients representing the same project.

Also, this idea of "bill group" could serve to crate groups of projects based on user-defined issues. But that's a more complex use case that perhaps exceeds this scraper.