bug 1331643: TAGGIT_CASE_INSENSITIVE=True

Tell django-taggit to use case insensitive lookups for existing tags.
We're using MySQL with a case insensitive collation, so this is already
done at the database level, but this may help the code work correctly
with the database.

kuma/settings/common.py

@@ -1433,3 +1433,6 @@ def get_user_url(user):
 # Tell django-recaptcha we want to use "No CAPTCHA".
 # Note: The API keys are located in Django constance.
 NOCAPTCHA = True  # Note: Using No Captcha implies SSL.
+
+# Tell django-taggit to use case-insensitive search for existing tags
+TAGGIT_CASE_INSENSITIVE = True