Allow economic AI to buy out/convert player cities that they've traded enough with

[DanGrizzly]

Hi, I'm not sure how you feel about others writing suggestions in your issues page, but I love the mod, and I thought it would be amazing if economic cities would be able to buy out cities they've traded with, since now a lot more economic cities spawn.

I noticed that in the description it says that Major Economic Nations can spawn but I can't seem to get it to happen.

I don't know how difficult it would be to fix that.

[DanGrizzly]

As silly as it is, I finally got it to happen on the 6th run. Sorry for writing the issue.

I've changed the title of the issue to focus on AI not being able to buy out player cities, as the progress bar for them doesn't even fill up. It would be interesting if the player had to reject or out-trade economic AI.