Abandoning could join AI

[dmcbride]

• Abandoning a colony should have a chance to have the colonists rebel and join an AI.
• Empires that expire should have a chance to have each colony join an AI
• Empires that self-destruct should also have a chance to have each colony join an AI

(Stations never join the AI? - this would only be relevant if the expiring/SD player were the last person in their alliance anyway.)

Which AI ... to be determined. Perhaps a weighted chance of joining any of a list of AIs? e.g., the equivalent of Saben, Cult, Diablotin, Trel, but not LEC or DeLambert?