[DEV-1152] Rename AskbotUserPassThroughManager to AskbotUserManager. Add custom get_query_set method which prefetches 'user' to reduce no. of queries performed.
[DEV-1152] Change regex match in middleware to string startswith.
[DEV-1320] Merge branch 'DEV-1152' into DEV-1320: get query pre-fetching and updated middleware.