Various small fixes in bridge and condenser api

Unused flag_weight column removed - fixed places where it was supposed to be computed

Fixed code that reads beneficiaries from operation

Changed error response from None to proper error in bridge.get_profile and bridge.get_post_header

Empty raw_json in hive_accounts no longer crashes API calls

condenser_api uses sum of payout and pending_payout for correct order by payout

When selecting blog posts with special start_index value (0 or -1) limit is shortened when there is not enough posts (was error which made no sense)