Allow editing of payment method on contribution edit form when no payments are associated
Currently, the contribution edit form does not allow editing of the payment method for a pending contribution. This may be useful for users, for example if someone fills out a contribution page with pay later and so their contribution payment method is set to check, but they will actually pay with an etransfer and we want to note this. It is also potentially confusing because the user can mark the payment as completed and record the payment two ways, by clicking Record Payment or by changing the status to completed, but only the first of these allows the user to change the payment method.
I think we can safely allow editing of the payment method when there are no payments associated with a contribution.