Debtlisting implemented

The debt for each participant is now shown. However it currently only
shows a standard value. This will be changed with some database calls.
Reduction of debt implemented

Now you can reduce the debt that registered persons have.
Some commented code, just so that it doesn't go all bananas before the
adding of debt has been implemented.
Basic debthandling implemented

Now debts are added when participants are registered to soups, and you
can manually subtract from the debt.
Minor Chances

Some minor changes in variable names and supression of warnings