Bugfix in migration

It turns out that we can have suggestions without user. We can't merge
those, so just skip them.
Migration: Also get rid of stale contenttype for suggestion model
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
Accounts: Add a custom User class
Accounts: Use full_name instead of first/last name
Accounts: Implement User.display_name
Accounts: Move gravatar_url() to User model
Accounts: Get rid of PootleProfileManager
Accounts: Get rid of the custom Profile admin
Accounts: Move PootleProfile.get_unit_rows to User.unit_rows
Accounts: Move UserForm to accounts.forms
Accounts: Move User.post_save logic to accounts

This lets us avoid a call to get_user_model() before the app registry is ready.
pootle_store: Pass User instances instead of PootleProfile wherever possible
Store: Use user instead of profile in get_alt_src_langs()