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/controllers/admin/sponsors_controller.rb

@@ -1,22 +1,55 @@
 module Admin
   class SponsorsController < Admin::BaseController
     load_and_authorize_resource :conference, find_by: :short_title
-    authorize_resource :sponsor, through: :conference
+    load_and_authorize_resource :sponsor, through: :conference
 
     def index
       authorize! :index, Sponsor.new(conference_id: @conference.id)
     end
 
-    def update
-      if @conference.update_attributes(params[:conference])
-        redirect_to(admin_conference_sponsors_path(
-                    conference_id: @conference.short_title),
-                    notice: 'Sponsorships were successfully updated.')
+    def edit; end
+
+    def new
+      @sponsor = @conference.sponsors.new
+    end
+
+    def create
+      @sponsor = @conference.sponsors.new(sponsor_params)
+      if @sponsor.save
+        redirect_to(admin_conference_sponsors_path(conference_id: @conference.short_title),
+                    notice: 'Sponsor successfully created.')
       else
+        flash[:error] = "Creating sponsor failed: #{@sponsor.errors.full_messages.join('. ')}."
+        render :new
+      end
+    end
+
+    def update
+      if @sponsor.update_attributes(sponsor_params)
         redirect_to(admin_conference_sponsors_path(
                     conference_id: @conference.short_title),
-                    alert: 'Sponsorships update failed.')
+                    notice: 'Sponsor successfully updated.')
+      else
+        flash[:error] = "Update sponsor failed: #{@sponsor.errors.full_messages.join('. ')}."
+        render :edit
       end
     end
+
+    def destroy
+      if @sponsor.destroy
+        redirect_to(admin_conference_sponsors_path(conference_id: @conference.short_title),
+                    notice: 'Sponsor successfully deleted.')
+      else
+        redirect_to(admin_conference_sponsors_path(conference_id: @conference.short_title),
+                    error: 'Deleting sponsor failed! ' \
+                    "#{@sponsor.errors.full_messages.join('. ')}.")
+      end
+    end
+
+    private
+
+    def sponsor_params
+      params[:sponsor]
+    end
   end
 end