Fix/406 update participants

I did my best with this. I fixed the problem both in the sidebar and on the proposal itself. It's working for the case when the law isn't in the sidebar list, too. Unfortunately, I'm new to this combination of technology, so I'm sure my work is messier than it should be, so please correct me where necessary. 

In particular, the logic to append the citizen to the list of participants is duplicated. It seems to me that there should be a global list of laws, so this need only be updated once, but I couldn't find a single place to do this. Let me know how to improve!