This adds support for Stripe Promo Codes in the user checkout process.
Also adds a discounted field to User > Billing > Subscriptions to show the amount or percent discounted.
This does not currently add in support for creating promo codes in the Subscriptions interface (that will come at a later point in time). Instead a coupon can be created with a promo code right from the Stripe dashboard.
Due to putting the Stripe Elements HTML inside an if block in the
template, this caused state to be funky. As a result, calling
`this.stripe.createToken` failed to return a promise. Opted instead to
hide the elements via CSS for anonymous users to prevent this
showstopping bug.
Improves the subscription flow for anonymous users by making the routes available, and showing a login button. Clicking login from this page will save a `destination_url` cookie so that when logging in they're redirected back to the subscription page they were at.
Building off the foundation of using the Prices API, this PR adds the ability to create a one-time purchase plan for any product, which then can add a user to the specified plan group.
Some things to be aware of:
One-time purchases cannot have trials.
One-time purchases use the Invoice API instead of Subscriptions. Invoices are created then charged immediately.
Users should receive emails for these invoices directly from Stripe just like subscriptions.
Justin DiRose
Faizaan Gagan
Rimian Perkins