Add support for easily enabling the django debug toolbar

This requires the web server to also configure a static mapping for
/media/django_toolbar/ pointing into the django toolbar directories.

pgweb/settings.py

@@ -162,5 +162,15 @@ FRONTEND_SMTP_RELAY = "magus.postgresql.org"                # Where to relay use
 OAUTH = {}                                                  # OAuth providers and keys
 PGDG_ORG_ID = -1                                            # id of the PGDG organisation entry
 
+# For debug toolbar, can then be fully configured in settings_local.py
+DEBUG_TOOLBAR = False
+INTERNAL_IPS = [
+    '127.0.0.1',
+]
+
 # Load local settings overrides
 from .settings_local import *
+
+if DEBUG and DEBUG_TOOLBAR:
+    MIDDLEWARE.append('debug_toolbar.middleware.DebugToolbarMiddleware')
+    INSTALLED_APPS.append('debug_toolbar')

pgweb/urls.py

@@ -1,5 +1,7 @@
 from django.conf.urls import include, url
+from django.urls import path
 from django.views.generic import RedirectView
+from django.conf import settings
 
 import pgweb.contributors.views
 import pgweb.core.views
@@ -156,3 +158,10 @@ urlpatterns = [
     # Fallback for static pages, must be at the bottom
     url(r'^(.*)/$', pgweb.core.views.fallback),
 ]
+
+
+if settings.DEBUG_TOOLBAR:
+    import debug_toolbar
+    urlpatterns = [
+        path('__debug__/', include(debug_toolbar.urls)),
+    ] + urlpatterns