Completely rework the navigation

Get rid of the admin layout
Get rid of the navbar custom style, use bootstrap-sass variables instead
Get rid of all the scaffold files

app/views/admin/conference/_sidebar.html.haml

@@ -1,5 +1,8 @@
 .well.sidebar-nav
   %ul.nav.nav-list
+    %li.nav-header
+      =@conference.short_title
+      Settings
     - if activated == "Conference"
       %li.active= link_to "Conference", "#"
     - else