LP 1198465: More tests for conditional negative balances

LP 1198465: More tests for conditional negative balances

This commit adds the remaining test cases documented by Kathy Lussier on
this wiki page:

    http://evergreen-ils.org/dokuwiki/doku.php?id=qa:billing_test_cases

Test cases included in this commit are:

    6. Restores Overdue Fines Appropriately, No Previous "Voids", Patron
       Will Not Owe On Lost Item Return
    7. Restores Overdue Fines Appropriately, No Previous "Voids", Patron
       Will Still Owe On Lost Item Return
    9. Restore Overdue Fines Appropriately, Previous Voids, Negative
       Balance Allowed
   13. Prohibit negative balances on lost materials bills ONLY
   14. Prohibit negative balances on overdue bills ONLY

Note that test case 5 is omitted because it is a duplicate of case 2,
and case 11 is included but commented out because it is unclear how best
to handle the situation.

Signed-off-by: Remington Steed <rjs7@calvin.edu>
Signed-off-by: Dan Wells <dbw2@calvin.edu>