AIMode effects

[Iceman]

As promised, here's a list of the current effects of AIMode in the game.

Normal:
- will not build SYs in small systems
- takes longer (rng) between diplomatic proposals
- builds less colony ships to finish terraforming colonized systems

Hard and Impossible:
- doesn't care if another civ is already terraforming an uncolonized system
- will colonize immediately upon arrival of another empire's colony ship
- will target systems for colonization even if another empire's colony ship is there
- Borg probes will use the Intercept order
- [Hard] Warlike minor civs will always engage
- [Impossible] Warlike and Raider minor civs will always engage

Normal vs Hard vs Impossible:
- increasing initial rank of spawned AI ships
- increasing limit for colony ship construction
- increasing limit for warship construction
- decreasing effects of credits/resources gifts
- increasing bribe resistance
- increasing penalty for colonizing system / building station on borders


Feedback and ideas on how to improve / add to this are welcome.