Make ticket layout configurable

spec/factories/conferences.rb

@@ -10,6 +10,7 @@ FactoryGirl.define do
     start_hour 9
     end_hour 20
     registration_limit 0
+    ticket_layout 0
     description { Faker::Hipster.paragraph }
     organization
     after(:create) do |conference|

spec/models/conference_spec.rb

@@ -1573,6 +1573,10 @@ describe Conference do
       should validate_presence_of(:end_hour)
     end
 
+    it 'is not valid without a ticket_layout' do
+      should validate_presence_of(:ticket_layout)
+    end
+
     it 'is not valid with a duplicate short title' do
       should validate_uniqueness_of(:short_title)
     end