adding public activity gem and database migrations

Gemfile

@@ -142,3 +142,4 @@ gem 'active_model_serializers'
 # limit the number of requests by user to api
 gem 'redis-throttle', git: 'git://github.com/lelylan/redis-throttle.git'
 
+gem 'public_activity'
\ No newline at end of file

db/migrate/20160503140557_create_activities.rb

+# Migration responsible for creating a table with activities
+class CreateActivities < ActiveRecord::Migration
+  # Create table
+  def self.up
+    create_table :activities do |t|
+      t.belongs_to :trackable, :polymorphic => true
+      t.belongs_to :owner, :polymorphic => true
+      t.string  :key
+      t.text    :parameters
+      t.belongs_to :recipient, :polymorphic => true
+
+      t.timestamps
+    end
+
+    add_index :activities, [:trackable_id, :trackable_type]
+    add_index :activities, [:owner_id, :owner_type]
+    add_index :activities, [:recipient_id, :recipient_type]
+  end
+  # Drop table
+  def self.down
+    drop_table :activities
+  end
+end