Introduces new audience object

#416

db/migrate/20140804185823_create_audiences.rb

@@ -0,0 +1,12 @@
+class CreateAudiences < ActiveRecord::Migration
+  def change
+    create_table :audiences do |t|
+      t.integer :conference_id
+      t.date :registration_start_date
+      t.date :registration_end_date
+      t.text :registration_description
+
+      t.timestamps
+    end
+  end
+end