Olefloch/wfu 3482/readonly mode]

To test, add the SITE_READ_ONLY to your local_settings file (see README).

When set to False, all requests should behave as before.
When set to True, all GET requests should work properly, but not create Clicks, and requests to the api should fail with a 503 error.

Also, this pull requests prevents POST requests to redirection urls, and GET requests to the shortener itself (I checked and the work for us properly sends POST requests already).