Feature/stripe

[Firgrep]

Building Stripe integration and other minor changes

Checklist

• [x] finish webhook
• [x] additional email to admin for successful purchases
• [x] add email response for successful purchase
• [x] seminar and dialogue tiers are additionally controlled by date on both frontend and backend
• [x] add stripe checkout for products
  • [x] build a server component version of course card
  • [x] add a check on whether or not the user owns the course
  • [x] build stripe checkout function for unowned courses on serverside
• [x] add image upload to bucket on course creation (this does not need to be made private, so easier to manage)
• [x] send the url of the course image to the stripe product (and make sure it updates with the image)
• [x] polling mechanism for successful purchases

closes #19, closes #21, closes #45, closes #46,