Pledge schedule data lost when unrelated edits are done

The pledge form deletes & recreates pledge payments when the pledge is edited. This makes sense when editing the schedule but it also happens when editing fields that do not affect the schedule, if the pledge is pending.

Since it's possible to edit the schedule to a custom schedule by editing the payments this data should be protected unless the edit affects a scheduled payment field - ie.

'amount',
'frequency_unit',
'frequency_interval',
'frequency_day',
'installments',
'start_date',

Supplied patch checks if any of the above fields are being edited & only deletes the payment if one or more is changed