Allow setting filters for events on the damage done for on_entity_damaged

[randomdude]

Use cases:

- Biters seem to trigger on_entity_damaged walking around and crashing into each other. However, all these events are always 0 final_damage_amount, and hence, not that useful imo
- Spitters shooting walls trigger it too, and i guess the reduction or something is triggering 0 final_damage_amount also.


Alternatively, would just skipping events that will do 0 final damage have any bad consequence?

[Bilka]

Okay, I added "original-damage-amount", "final-damage-amount" and "damage-type" filters to the on_entity_damaged event filters for the next version. Although the damage system is now automatically skipped for damage of 0 (viewtopic.php?p=472758#p472758), it may still be useful in other cases.