Django-email-signals

* A bug where CSS files were not loading in the admin page has been resolved.

* When retrieving signal constraints we were previously filtering by a signal's content type using the `Signal.objects.get` method. However, there can been multiple `Signal` instances for a single content type. This therefore would cause an error. This has been fixed by retrieving the signal constraints from the `Signal` instance directly.

* `mailing_list` now accepts a comma separated list of email addresses as well as a function that would return a list of email addresses.

* Fixed Django requirement in setup.cfg

1.0.4: Ability to add context to plain and HTML fields.
- Added the ability to add context to the plain and HTML fields.

* Fixed bug where certain fields could not be accessed in a model when saving signal constraints.
* Allowed `created` as a valid value for `param_1` in the signal constraints form.

* Now supports [django-grapelli](https://django-grappelli.readthedocs.io/en/latest/).