dev-python/django: bump to 2.1

dev-python/django: bump to 2.1

* EAPI 7
* Drop py34
* Add py37
* Drop webapps

Inheriting webapps doesn't make sense. This isn't a webapp, it's a
library. Because django was abandoned before I took over maintenance, I
highly doubt that the package was used for anything serious, so there
isn't much to break by this removal.

The only thing that webapps did was copy admin media in some place for
easy HTTP static serving, but that isn't even what you would want to do
in a django webapp. You would rather run "collectstatic" on the whole
app and serve the result, which would include admin media, over HTTP.

Package-Manager: Portage-2.3.44, Repoman-2.3.10