small cubbies app scope refactor

app/controllers/apps_controller.rb

@@ -1,12 +1,8 @@
 class AppsController < ApplicationController
   def show
     @app = 'cubbies'
-    @posts = ActivityStreams::Photo
     max_time = params[:max_time] ? Time.at(params[:max_time].to_i) : Time.now
-    @posts = @posts.where(ActivityStreams::Photo.arel_table[:created_at].lt(max_time)
-                         ).where(:public => true
-                         ).order('posts.created_at DESC'
-                         ).includes(:author => :profile).limit(30)
+    @posts = ActivityStreams::Photo.where(:public => true).for_a_stream(max_time, 'created_at')
     @commenting_disabled = true
     @people = []
     @people_count = 0