Change the app_usages API to accept array of data

- Add foreignkey to device for AppUsage
- Rename the route to app_usage from app_usage/create

db/migrate/20160204094618_create_app_usages.rb

@@ -4,7 +4,8 @@ class CreateAppUsages < ActiveRecord::Migration
       t.string :package_name, null: false, index: false
       t.integer :usage_duration_in_seconds, null: false, index: false
       t.date :used_on, null: false, index: false
-
+      t.belongs_to :device, foreign_key: true, index: true
+      
       t.timestamps null: false
     end
   end