Merge pull request #615 from hennevogel/master

Implements sign up during registration. Solves most of #215

app/models/ability.rb

@@ -121,6 +121,10 @@ class Ability
     can :show, Commercial, commercialable_type: 'Event', commercialable_id: Event.where(state: 'confirmed').pluck(:id)
     # can view others
     can :show, User
+    # can register
+    can [:read, :create], Registration do |registration|
+        registration.new_record?
+    end
   end
 
   def signed_in(user)

app/models/registration.rb

@@ -1,5 +1,7 @@
 class Registration < ActiveRecord::Base
   belongs_to :user
+  validates :user, presence: true
+  accepts_nested_attributes_for :user
   belongs_to :conference
   belongs_to :dietary_choice