Loans++

- A number of fixes applied to the recent loans changes
- AI is ready to actually use loans, intelligently and aggressively borrowing when funds are exhausted, repaying as promptly as possible, and just maintaining minimum payments when it's expedient.  Both the decisions and the annual event have been outfitted appropriately
- Optional tracing support for observing long-term aggregate AI debt management behavior (do they promptly pay their debts off, do they get into a downward spiral of debt racking-up, how much are they in debt in time-series, how much interest is paid over an average ruler's lifetime, etc.) instrumented throughout the loans code
- Took care of some oversights that would've allowed some silly and abusive things now that the AI is allowed to take loan decisions