Bug 23788: Recalculate ammount due for selected accountlines

Bug 23788: Recalculate ammount due for selected accountlines

Individual fees cannot be overpaid of over-written off, but it's possible to 'overpay' a writeoff of selected fees.

Test Plan:
1) Create 3 fees
2) Pick 2 and choose "Write off selected"
3) Write off more than the total amount of those fees
4) Apply this patch set
5) Restart all the things!
6) Try again, you should no longer be able to!

Signed-off-by: Sean McGarvey <seanm@pascolibraries.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>