FEATURE: Allow one-time purchases on products (#18)

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.

assets/javascripts/discourse/components/payment-options.js.es6

@@ -1,22 +1,9 @@
-import { equal } from "@ember/object/computed";
 import Component from "@ember/component";
 
 export default Component.extend({
-  planButtonSelected: equal("planTypeIsSelected", true),
-  paymentButtonSelected: equal("planTypeIsSelected", false),
-
   actions: {
-    selectPlans() {
-      this.set("planTypeIsSelected", true);
-    },
-
-    selectPayments() {
-      this.set("planTypeIsSelected", false);
-    },
-
     clickPlan(plan) {
-      this.plans.map(p => p.set("selected", false));
-      plan.set("selected", true);
+      this.set("selectedPlan", plan.id);
     }
   }
 });

assets/javascripts/discourse/components/payment-plan.js.es6

@@ -0,0 +1,23 @@
+import Component from "@ember/component";
+import discourseComputed from "discourse-common/utils/decorators";
+
+const RECURRING = "recurring";
+
+export default Component.extend({
+  @discourseComputed("selectedPlan")
+  selected(planId) {
+    return planId === this.plan.id;
+  },
+
+  @discourseComputed("plan.type")
+  recurringPlan(type) {
+    return type === RECURRING;
+  },
+
+  actions: {
+    planClick() {
+      this.clickPlan(this.plan);
+      return false;
+    }
+  }
+});