PCP notification email should not be sent when contribution record is updated UNLESS a new PCP soft credit is added

Modify the PCP Owner notification code to only send the notification when a PCP-based soft credit is CREATED. Do not trigger notification via contribution edit UNLESS a new PCP soft credit is added as part of the update.

NOTE: This would cover the use case I describe in my comment below (PCP link is added to existing contribution OR recorded when an offline contribution is created) as well as the original use case (online contribution submitted via a PCP page).

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Steps to reproduce the 'bug':

1. Set up a personal campaign page with notification emails being sent to the page owner
2. Make a contribution through the PCP
3. Observe that the message from template "Personal Campaign Pages - Owner Notification" is sent to the page owner (good!)
4. Edit the contribution and mark it as refunded
5. Expect that no further email messages will be sent to the page owner
6. Observe that the page owner receives an email that is 100% identical to the original email.

When a refund needs to be issued (which, in my experience often the page owner is aware of), this bug makes the page owner think that instead of the refund going through, the donor has been charged again. This leads to a small amount of panic and frustration from the page owner.