[ABW]: [Fix] payout related vops are handled with current block timestamp...

[ABW]: [Fix] payout related vops are handled with current block timestamp instead of head block time (also commented why it most likely worked like that in 0.23)
[Fix] typo in fork rewind code
[Fix] replaced 1990-01-01 with 1970-01-01 (minimum timestamp) as default in various places where it indicates 'not set' state
[Ign] removed unused last_payout column from hive_posts (the related data was taken from payout_at)