Accounts: Get rid of PootleProfile.*_suggestion_count()
Accounts: Use AUTH_USER_MODEL in all User migration relations
initdb: Create directories before creating essential users

This fixes the issue of Directory.objects.root being called before
other models are loaded
Accounts: Use settings.AUTH_USER_MODEL in PootleProfile as well
Accounts: Get rid of is_staff everywhere
pootle_store/views: Simplify user/profile logic
docs: Get rid of a soon-to-be irrelevant warning in the api docs
Profile: Display profile email for admin users
refresh_stats: Add some additional prints to report progress
refresh_stats: Marginal performance improvement on large projects
Stats: Add fields to cache last created unit and last submission

This will improve performance when retrieving the stats table.
Stats: Update last created unit

Current approach will increase load when adding whole new stores,
translation projects and projects.
Stats: Update last submission
refresh_stats: Update last unit and last submission fields
Stats: Update and retrieve cached unit and submission