Work in current profits into a credit rating bonus

[Eric B Jones]

https://steamcommunity.com/app/285110/discussions/0/1741105805764113711/

Take last 6 months profits and use that for up to a +1 bonus to credit rating.

[Eric B Jones]

Would add a bunch of extra code to the credits system. Instead I adjusted the values so that a higher credit rating is more likely.