Paypal should be PayPal; a brand name should be a placeable

[peiying2]

File: main.ftl
Problem: Paypal should be treated like a brand name, a placeable, and should be spelled correctly - capital Ps.

## payment legal blurb
payment-legal-copy-stripe-paypal = { -brand-name-mozilla } uses Stripe and Paypal for secure payment processing.
payment-legal-link-stripe-paypal = View the Stripe privacy policy and Paypal privacy policy.

After the release of the settings.ftl, let's standardize the treatment of these brand names.

@chenba

[clouserw]

This will appear in this repository next Friday. Thanks