- Defined hive.get_balance_impacting_operations() useful to limit number of...

- Defined hive.get_balance_impacting_operations() useful to limit number of operations to be processed for balance tracking
- Schema of btracker tables extended by block_num, to prepare for read APIs which can query for data specific to given block.
- Changed PK of btracker.account_balance_history due to blockchain bugs accepting a self transfer.