Siren Weight Adjust & Required Crew Fix

[WeNeedMorePhoron]

About The Pull Request

• Adjust siren weight to 0.25 and required crewmember to 12 (Instead of the intended 8 which ended up as a de facto 8).
• Remove the max_crew_diff_lower variable which defaulted to 10, leading to all event without it set explicitly having 10 lower required crew than expected.

Why It's Good For The Game

Make Siren no longer fire on low pop, lower its chance of firing. Also align coder expectations of req_crew blocking events firing on low pop round with what is happening.

CHANGES: Because of these changes, numerous event's actual required crew has been adjusted upward. I am open to feedback to changing it back.

• Malf AI now fire on min. 15 pop instead of 10 pop (might need adjustment?)
• Marshal fire on min. 10 pop instead of 0 pop
• Mercenary fire on min. 5 pop instead of -5 pop
• Siren fire on min. 12 pop instead of 5 pop

Changelog

tweak: Siren have half the initial weight and can only fire when there's 12 crew or more 
tweak: Malf AI now fire on minimal 15 pop instead of 5 pop. 
tweak: Marshal now fire on minimum 10 pop and mercenary 5 instead of 0 / -5 which was not working as intended. (These events can fire but fail to find a target)

[Jamini]

Your changes do not do what you think they do, and this removes the scaling percentage below ideal population.