REFACTOR: Use models to store data (#11)

* REFACTOR: Use api to add subscribe link

* FIX: I18n subscribe link

* REFACTOR: Use models to store some data

This enables the plugin to show only subscription information which was
generated on Discourse. Subscription data storage is limited to the
external identifiers Stripe generates so we can interact with the API.

* DEV: Test/linting fixes/rake task

plugin.rb

@@ -4,7 +4,7 @@
 # about: Integrates Stripe into Discourse to allow visitors to subscribe
 # version: 2.8.1
 # url: https://github.com/discourse/discourse-subscriptions
-# authors: Rimian Perkins
+# authors: Rimian Perkins, Justin DiRose
 
 enabled_site_setting :discourse_subscriptions_enabled
 
@@ -45,7 +45,7 @@ after_initialize do
   ::Stripe.set_app_info(
     'Discourse Subscriptions',
     version: '2.8.1',
-    url: 'https://github.com/rimian/discourse-subscriptions'
+    url: 'https://github.com/discourse/discourse-subscriptions'
   )
 
   [
@@ -67,6 +67,8 @@ after_initialize do
     "../app/controllers/products_controller",
     "../app/controllers/subscriptions_controller",
     "../app/models/customer",
+    "../app/models/product",
+    "../app/models/subscription",
     "../app/serializers/payment_serializer",
   ].each { |path| require File.expand_path(path, __FILE__) }