2FA: Enable Django template backend.

The only purpose of this commit is to make the django templates
of Two Factor Auth work. We probably won't need this commit once
we upgrade the admin backend of Two Factor Auth to use handlebar
templates.

zproject/settings.py

@@ -491,6 +491,12 @@ ALLOWED_HOSTS += [EXTERNAL_HOST.split(":")[0],
 # ... and with the hosts in REALM_HOSTS.
 ALLOWED_HOSTS += REALM_HOSTS.values()
 
+from django.template.loaders import app_directories
+class TwoFactorLoader(app_directories.Loader):
+    def get_dirs(self):
+        dirs = super(TwoFactorLoader, self).get_dirs()
+        return [d for d in dirs if 'two_factor' in d]
+
 MIDDLEWARE = (
     # With the exception of it's dependencies,
     # our logging middleware should be the top middleware item.
@@ -1193,11 +1199,27 @@ non_html_template_engine_settings['OPTIONS'].update({
     'lstrip_blocks': True,
 })
 
+# django-two-factor uses the default Django template engine (not Jinja2), so we
+# need to add config for it here.
+two_factor_template_options = deepcopy(default_template_engine_settings['OPTIONS'])
+del two_factor_template_options['environment']
+del two_factor_template_options['extensions']
+two_factor_template_options['loaders'] = ['zproject.settings.TwoFactorLoader']
+
+two_factor_template_engine_settings = {
+    'NAME': 'Two_Factor',
+    'BACKEND': 'django.template.backends.django.DjangoTemplates',
+    'DIRS': [],
+    'APP_DIRS': False,
+    'OPTIONS': two_factor_template_options,
+}
+
 # The order here is important; get_template and related/parent functions try
 # the template engines in order until one succeeds.
 TEMPLATES = [
     default_template_engine_settings,
     non_html_template_engine_settings,
+    two_factor_template_engine_settings,
 ]
 ########################################################################
 # LOGGING SETTINGS