Lowers the manifest requirement for biohazards to ~20

[MixityMaxity]

What Does This PR Do

Lowers the required amount of active crew on the manifest needed to spawn a biohazard to be around 20, also removes the extra 50 manifest hardcap on xenos.

additionally lowers the expected requirements on both security and medical by a bit, as a majority of the crew is intended to contribute to these.

Why It's Good For The Game

Given the current situation when it comes to population and disaster events, most rounds end up quite boring and basically extended slog over and over, even with antags. Biohazards were, and still are one of the most effective ways to actually add to the round, allowing everyone in the game to experience the round, including dchat and dead crew.

Xenos and blob have received sizeable nerfs in other PRs, primarily the remove of the xeno revival nest, making xeno numbers purely strategy and infecting actual hosts, instead of reviving the entire alien force again and again. Blob had their ability to split core below 60 pop removed, effectively halving resources and management in lower pop rounds. Terrors are in a pretty good place right now.

Yes this will likely lead to more rounds ending in nuke/shuttle/station loss, but that really isnt a bad thing, having a shift procced the exact same each and every time gets boring for everyone.

Testing

• Attempted to repeatedly spawn disaster events with one player on manifest, rolled nothing constantly
• Forced a blob, xeno and spooder spawn to ensure they all spawned correctly
• Fed some skrell to the biohazards
• More testing will be required in a test merge, to ensure these changed values actually work and are balanced

Declaration

• I confirm that I either do not require pre-approval for this PR, or I have obtained such approval and have included a screenshot to demonstrate this below.

Changelog

🆑
del: Removed Xeno 50 manifest hardcap
tweak: Changed the role requirements on Xenos, Blob and Terrors
/:cl: