Bug 22359: Improvements to payment collection inputs

Bug 22359: Improvements to payment collection inputs

This patch attempts to clarify the uses of the various input fields on
the paycollect screens.

It does this by adding validation to the form such that entering a
'collected' value that is lower than the 'paid' value is now forbidden.

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>