Fix #708 - Open PayPal inside the Facebook when donating

[maxxcrawford]

Summary

This patch adds logic to open up a PayPal window inside the Facebook Container if the origin URL is https://facebook.com/donate and allows PayPal resources to be loaded inside Facebook Container.

Privacy Considerations:

• Does this patch leak info for users who have both PayPal and Facebook accounts but do not connect services?
• Current allowed resources from PayPal include a wild card for subdomains. Is that okay?

Testing Steps

• Log into Facebook
  • Note - Make sure you do not have PayPal already connected as a funding source
• Go to https://www.facebook.com/fundraisers/ and select any active campaign
• Click "Donate" button
• Under the Payment Method section, select "Connect to PayPal"
• Click blue "Donate" button at the bottom of the form
• EXPECTED: A separate PayPal window should open and be INSIDE the Facebook Container