- UserApp.currentUser create user object using cookie when there is no
  session data
- utils.BasicAuthAction is edited because
  UserApp.authenticateWithPlainPassword does not return null anymore
- add tests

application.context should be taken into account while computing the url
to user's avatar.

Third-party libraries are excepted.

* In test-data.yml, Remove entities already added by initial-data.yml.
* Make Global.insertTestData insert "users" entities.

Author can delete own issue or posting regardless of config