Campaign chassis modoption

[sprunk]

FYI: the campaign_chassis modoption now allows the AI to choose dyntrainer_knight_base as comm chassis - this is the campaign commander who can mount all weapons and modules.

I think it is undesirable to use on Normal and below (nubs like to feel special), but feel free to use it on Hard+ if you want to (the chassis has fairly mediocre base stats so it might require figuring out some OP combos to present a challenge).

[rlcevg]

Current picking system has no way to tell if a unitDef is ploppable. It relies only on AI's config assuming that any unitDef described in commander section is valid to pick.
So to make commander picking versatile a call to lua that returns all possible starting units has to be added, i think. With such function AI will be able to filter out false unitDefs (and not rely on signle-purpose variables like campaign_chassis).
Or some dynamically set customParam on unitDef can also tell if commander is ploppable, no lua call needed.

[sprunk]

Custom param sounds like a good idea, will do.

[sprunk]

Added a customParam, ai_start_unit, to starting units the AI can pick.