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/views/admin/registrations/edit.html.haml

@@ -1,8 +1,8 @@
 .row
   .col-md-12
-    %h3
-      Edit registration of #{@user.name} (#{@user.email}) for #{@conference.title}
-      %br
+    .page-header
+      %h1
+      Edit registration of #{@user.username} for #{@conference.short_title}
 .row
   .col-md-8
     = semantic_form_for(@registration, :url => admin_conference_registration_path(@conference.short_title, @registration)) do |f|