Display kill assists by players & bots.

Kill assists are whoever (other than the killer) did most damage.
In the case of a tie, the most recent is used.

(Currently, this code re-uses groundEntityNum via a macro for the assistant.)
Require reported assists to be for ≥ min(killer damage, 25%).
Move alien spawning position closer to the egg bounding box.
Don't report assistants for suicides.
Turret health 190 → 250, price 8 → 10. Armoury price 10 → 8.