check that the username field has the focus on login page
refactor caffeine test modules

- move tests into module directory
- split authentication tests into separate methods for each concern
- add placeholder files for model, form and view tests
add tests for middleware
add tests for template tags
add tests for caffeine.models.CaffeineUserManager

- refactor caffeine.models.CaffeineUserManager.create_user and
  .create_superuser to properly fill is_staff and is_superuser fields
- add test class in caffeine.tests.test_models
remove empty files from caffeine_api_v1
add test class for caffeine.models.User

- fix typo in caffeine.models.User.export_csv
- add caffeine.tests.test_models.UserTest
mark private helpers in caffeine.models