You have to list the plugins in your INSTALLED_APPS as well, see:
https://github.com/benjaoming/django-wiki#configure-settingsinstalled_apps
So your INSTALLED_APPS should contain, in this order:
'django.contrib.humanize',
'south',
'django_notify',
'mptt',
'sekizai',
'sorl.thumbnail',
'wiki',
'wiki.plugins.attachments',
'wiki.plugins.notifications',
'wiki.plugins.images',
'wiki.plugins.macros',
EDIT:
I'd suggest re-installing the wiki package.
# pip uninstall wiki
# pip install wiki