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/difficulty_levels/index.html.haml

@@ -1,6 +1,33 @@
 .row
-  .col-md-8
-    = semantic_form_for @conference, :url => admin_conference_difficulty_level_path(@conference.short_title, @conference.difficulty_levels) do |f|
-      = f.input :use_difficulty_levels, :label => false
-      = dynamic_association :difficulty_levels, "Difficulty_Levels", f
-      = f.action :submit, :as => :button, :button_html => {:class => "btn btn-primary"}
+  .col-md-12
+    .page-header
+      %h1 Difficulty Levels
+      %p.text-muted
+        Classify your conference events by difficulty
+.row
+  .col-md-12
+    %table.table.table-hover#difficulty_levels
+      %thead
+        %th Title
+        %th Description
+        %th Color
+        %th Actions
+      %tbody
+        - @conference.difficulty_levels.each do |difficulty_level|
+          %tr
+            %td
+              = difficulty_level.title
+            %td
+              = difficulty_level.description
+            %td
+              %span.label{style: "background-color: #{difficulty_level.color};"}
+                = difficulty_level.color
+            %td
+              .btn-group{role: "group"}
+                = link_to 'Edit', edit_admin_conference_difficulty_level_path(@conference.short_title, difficulty_level.id),
+                method: :get, class: 'btn btn-primary'
+                = link_to 'Delete', admin_conference_difficulty_level_path(@conference.short_title, difficulty_level.id),
+                method: :delete, class: 'btn btn-danger', data: { confirm: "Do you really want to delete #{difficulty_level.title}?" }
+.row
+  .col-md-12.text-right
+    = link_to 'Add Difficulty Level', new_admin_conference_difficulty_level_path(@conference.short_title), class: 'btn btn-primary'