Provide a custom User implementation

[luzfcb]

Migrating from the standard User implementation to a custom implementation can be (extremely) complex In an existing project. We should provide a minimal custom User implementation so that any further changes are simpler to make.

[luzfcb]

cookiecutter-django implements a custom user (although it makes some decisions that fall outside the django standard, like having a name field instead of first_name and last_name, since the first_name and last_name pattern may not make sense in many languages )

https://github.com/pydanny/cookiecutter-django/tree/master/%7B%7Bcookiecutter.project_slug%7D%7D/%7B%7Bcookiecutter.project_slug%7D%7D/users