Add surveys; custom generated by admins

Available during registration or after conference

Co-authored-by: Shyukri <shshyukriev@suse.com>
Co-authored-by: Henne <hvogel@opensuse.org>
Co-authored-by: Moises <mdeniz@suse.com>

db/migrate/20160627122446_create_surveys.rb

@@ -0,0 +1,13 @@
+class CreateSurveys < ActiveRecord::Migration
+  def change
+    create_table :surveys do |t|
+      t.datetime :start_date
+      t.datetime :end_date
+      t.string :title
+      t.text :description
+      t.references :surveyable, polymorphic: true, index: true
+
+      t.timestamps null: false
+    end
+  end
+end