This change updates the Review Bot extension to handle deprecated and

changed APIs for Django 1.11 and Python 3. These include:

URL patterns are now defined as lists instead of using the old

patterns object.
Django used to ship a backport of Python 2.7's import_module, which

  is no longer included. Since we are now 2.7+ only, we can use the

  standard library version.
ModelForm needs to define Meta.fields.
Models need to define app_label, especially in the extension context

  where the module is not listed in INSTALLED_APPS.
The ToolOptionsWidget.format_output method was removed, seemingly

  without explanation (despite being recommended as something that could

  be overridden in the comments). Since we're completely overriding

  the widget's render method, this has been changed to just do what

  the old format_output method did.
Python 3's __import__ needs to use native strings rather than bytes.

Set up the Review Bot extension on my local devserver using the latest

Review Board release-4.0.x HEAD and Python 3, and connected a worker.

Configured an integration for jshint and published a review request. Saw

that Review Bot triggered the worker job, collected errors, and posted

them back to the review request.