Make the Django login button appear in Swagger

[waxlamp]

If you accidentally clobber the SWAGGER_SETTINGS value (e.g., as Multinet does) then the Swagger page shows a Django login button and a basic auth button. The basic auth button is wrong, but the Django login button is useful.

A quick look at the code for YASG's swagger page template shows that the Django login button ought to be shown under the current configuration settings, but it doesn't. We should figure out why, because that login button adds a nice amount of value to Girder4 projects.