Add GCM push for pushing OneMDM app to devices

db/migrate/20151113131647_create_batch_installations.rb

@@ -1,8 +1,7 @@
 class CreateBatchInstallations < ActiveRecord::Migration
   def change
     create_table :batch_installations do |t|
-      t.integer :app_id
-
+      t.belongs_to :app, foreign_key: true, index: true
       t.timestamps null: false
     end
   end