Authorize access to admin panel, etc.

Adds a separate admin namespace and base controller, with authorization
by looking up the admin property in the user's LDAP account.

app/controllers/application_controller.rb

@@ -8,4 +8,15 @@ class ApplicationController < ActionController::Base
       redirect_to welcome_path and return
     end
   end
+
+  def authorize_admin
+    http_status :forbidden unless current_user.is_admin?
+  end
+
+  def http_status(status)
+    respond_to do |format|
+      format.html { render template: "shared/status_#{status.to_s}", status: status }
+      format.any  { head status }
+    end
+  end
 end