parsemail: Convert to a management command

parsemail: Convert to a management command

Management comands allow applications to register their own actions
with 'manage.py'. This provides some advantages, like automatically
configuring Django (removing the need for 'django.setup' calls) and
removing the need to set the PYTHON_PATH. The 'parsemail' script is a
natural fit for this type of application. Migrate 'parsemail' to a
management command.

This includes some extensive work on logging configuration, as logging
is moved from code into settings. In addition, it removes a lot of the
customizable logging previously introduced in the parsemail command, in
favour of modifications to the settings files.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Stephen Finucane <stephen@that.guru>
Partial-bug: #17
Closes-bug: #15