All available fills incorrect amount on loan repayment screen

[snollygolly]

Even though I tried to make things better with #65, it has its own problems now. I think ultimately, when clicking "all available", it should be the amount in the bank as long as that amount is less than or equal to the amount of the loan. If the amount in the bank is greater than the loan, the amount that shows up when clicking "all available" should be the loan amount.