Update management commands for Django 1.11 compatibility and modern standards.

Review Request #10476 — Created March 29, 2019 and submitted — Latest diff uploaded

Review Board

This updates all of the management commands to be compatible with both
Django 1.6 and 1.11, using the compatibility layer in Djblets. The major
differences between these releases is that there's only a BaseCommand
class, rather than a NoArgsCommand subclass (which wasn't even
important in Django 1.6), and that option parsing uses argparse
instead of optparse (which the Djblets compatibility class bridges for

Many of the commands have also been updated to meet modern coding
standards. This includes doc strings, localization, and small style
tweaks. Not all of the commands received this treatment. Some are
scheduled to be removed, and others (like fill-database) requires a
larger amount of work than was intended for this change.

Tested each management command individually on Django 1.6 and 1.11.