settings: Use explicit setup for the Debug Toolbar

settings: Use explicit setup for the Debug Toolbar

The 'django-debug-toolbar' application provides an automatic method of
configuring the plugin. However, as noted in the documentation [1],
this can cause issues like circular imports. In this case, a
"Table 'patchwork.patchwork_state' doesn't exist" exception was being
raised when attempting to do an initial migration.

Resolve this by using the manual configuration provided in the docs.

[1] https://django-debug-toolbar.readthedocs.org/en/1.4/installation.html

Signed-off-by: Stephen Finucane <stephen.finucane@intel.com>
Closes-bug: #29
---
v2: Don't rely on 'settings.DEBUG', as this is set to False in tests