Implement some condenser methods

- get_following
- get_hardfork_version
- get_key_references
- get_next_scheduled_hardfork
- get_reblogged_by
- get_reward_fund
- get_ticker
- get_vesting_delegations
- get_volume
- get_witness_count
- is_known_transaction
- lookup_accounts
- lookup_witness_accounts