feat(purchase/): add purchase app

purchase/models.py

@@ -0,0 +1,9 @@
+from django.db import models
+from django.conf import settings
+
+
+class CoursePurchase(models.Model):
+    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
+    course = models.ForeignKey("home.CoursePage", on_delete=models.CASCADE)
+    purchased_at = models.DateTimeField(auto_now_add=True)
+    refunded = models.BooleanField(default=False)