[ABW]: changed the way follow list resetting works (closer to previous...

[ABW]: changed the way follow list resetting works (closer to previous solution but with separate SQL functions) since there should not be too many such operations
replaced constants with enum values for clarity
eliminated unnecessary subqueries (replaced with outer join) and internal order clause, simplified query loop
checks during validation reordered to exit earlier in case of fatal error
[Note] whole follow code most likely needs more test scenarios - to be added