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

us).
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.