Implement consistent admin interface

* Consistent route/model/controller/view layout
* Get rid of unused photos, speakers, dietchoices, social_events controllers
* Drop unused :public from Rooms and :description from CallForPapers

app/models/room.rb

@@ -1,5 +1,5 @@
 class Room < ActiveRecord::Base
-  attr_accessible :name, :size, :public, :conference_id
+  attr_accessible :name, :size, :conference_id
 
   belongs_to :conference
   has_many :events
@@ -10,8 +10,6 @@ class Room < ActiveRecord::Base
 
   validates :size, numericality: { only_integer: true, greater_than: 0 }, allow_nil: true
 
-  validates :size, presence: true, if: :public?
-
   private
 
   def generate_guid