[EPIC][Feature] Add Paypal as donation option

[igoychev]

Is your feature request related to a problem? Please describe.
Implement Paypal as donation option, to ease donations for people to donate through their paypal accounts instead of entering credit cards.

Describe the solution you'd like
Add a branded Paypal button as another option on Donation steps.

Describe alternatives you've considered
Currently payment method is selected using radio buttons, but when adding more payments may be we just need to list the branded payment buttons like Apple Pay and Paypal. Another option will be to have a dropdown with selecting the payment option.

Additional context
Paypal Developer portal: https://developer.paypal.com/home

[quantum-grit]

Status update:

• Integrate Paypal on Frontend and visible only for Admins in sandbox mode
• Integrate Paypal webhook on backend
• Implement new UI for all users
• Enable production mode