Add native push notification infrastructure

- Add action_push_native gem and SaaS configuration
- Add device registration API and UI
- Add User::Devices concern
- Add NotificationPusher::Native for push delivery
- Add tests and fixtures for native push

app/models/notification_pusher.rb

@@ -12,18 +12,22 @@ class NotificationPusher
     return unless should_push?
 
     build_payload.tap do |payload|
-      push_to_user(payload)
+      push_to_web(payload)
     end
   end
 
   private
     def should_push?
-      notification.user.push_subscriptions.any? &&
+      push_destination? &&
         !notification.creator.system? &&
         notification.user.active? &&
         notification.account.active?
     end
 
+    def push_destination?
+      notification.user.push_subscriptions.any?
+    end
+
     def build_payload
       case notification.source_type
       when "Event"
@@ -93,7 +97,7 @@ class NotificationPusher
       }
     end
 
-    def push_to_user(payload)
+    def push_to_web(payload)
       subscriptions = notification.user.push_subscriptions
       enqueue_payload_for_delivery(payload, subscriptions)
     end