[Printer] Move printer urlpatterns into optional urls

re2o/urls.py

@@ -73,7 +73,6 @@ urlpatterns = [
         r'^preferences/',
         include('preferences.urls', namespace='preferences')
     ),
-    url(r'^printer/', include('printer.urls', namespace='printer')),
 ]
 # Add debug_toolbar URLs if activated
 if 'debug_toolbar' in settings.INSTALLED_APPS:
@@ -85,3 +84,8 @@ if 'api' in settings.INSTALLED_APPS:
     urlpatterns += [
         url(r'^api/', include('api.urls', namespace='api')),
     ]
+
+if 'printer' in settings.INSTALLED_APPS:
+    urlpatterns += [
+        url(r'^printer/', include('printer.urls', namespace='printer')),
+    ]