Add party to VoteAction for agenda queries

@ofri & @orihoch , worked on this migration with @daonb . Please look at the file 0031 data migration.
The idea is to add party_id into VoteAction for agenda queries. The party_id is the party of the member at the time of the vote. This should make it easier and faster to run party queries on VoteAction objects (e.g. agendas).