Django Channels incompatibility

[Chiemezuo]

Introduction

As a result of the work done in #2228 , it is somewhat safe to say that the current state of the Debug toolbar does not currently support Django Channels. While further inspection needs to be done to ascertain the required changes to enable compatitbility, @tim-schilling and I suspect the problem is related to the middleware class(es) used by Django Channels.

Next Steps

• The PR can be shelved for now, but might be useful if/when work is done to enable compatibility.
• The documentation in the architecture.rst should include a disclaimer in the Problematic parts section that Django Channels is not yet compatible.
• The documentation in the Django Channels & Async section of installation.rst should be corrected to state that there is currently no support for Django Channels.