[SON-HIVE Voting] Refactor maintenance block processing to create multiple lists of active SONs, one per sidechain

The goal is to separate voting for Bitcoin and Hive SONs, so that they can act independently of each others. All code affected by this change should be refactored, in a way that enables that Bitcoin SON and Hive SON are considered separate entities.

Maintenance block processing should create list of active sons per sidechain, considering "per sidechain" votes, so only vote_id_bitcoin for a list of active sons for Bitcoin, and only vote_id_hive for a list of active SONs for Hive.