Scenario expansion

Mostly just adding stuff that I missed in the initial PR. 

-Allow forced/forbidden traits in scenarios: Done
-Limit start location choices based on scenario : In progress
-Various flags and starting conditions.
-Add more scenarios
What do you think about triggering limited starting locations based on having starting locations specified in the scenario?  If the scenario doesn't specify starting location(s), it gets the normal list, if it does specify only those locations are allowed.
If you go with a flag, how about "DEFAULT_STARTS" instead of "ALL_STARTS"?