Travis: Disable pytest
requirements: Update Django requirements
requirements: Update various requirements versions

Also drop exact versions for travis as we will always want the latest ones.
requirements: Update Raven optional dependency to 5.x
Travis: Always use latest packages from pypi
Travis: Use travis_retry for installing things
Travis: Cache apt packages
settings: Remove the INTERCEPT_REDIRECT option from dev settings

The option is deprecated on newer versions of django-debug-toolbar
Upgrade: Fix pootle imports
Permissions: Use User over PootleProfile
Permissions: Use User in get_matching_permissions()
Permissions: Change check_profile_permission() to check_user_permission()
Permissions: Minor style fixes
Accounts: Use settings.AUTH_USER_MODEL in PootleProfile as well
Accounts: Add a custom User class
Use full_name instead of first/last name
pootle_store/views: Simplify user/profile logic
Accounts: Get rid of PootleProfileManager
Accounts: Get rid of the custom Profile admin
Accounts: Move UserForm to accounts.forms