More granular database fixtures

[pelme]

A lot of issues reported would benefit from a more general approach to hooking into/overriding how pytest-django's internal fixtures with regard to managing the database. This issue is a place to collect related issues that should be solved when re-thinking/re-organizing the fixtures.

The (now quite old) branch https://github.com/pytest-dev/pytest-django/tree/fixturefix is the place where I have been experimenting with ideas in this area.

Support hooking into database creation:

• alternative database setup shemes #37 - alternative database setup schemes - use copy with sqlite / CREATE DATABASE foo TEMPLATE template0;
• xdist disable suffix #98 - disable xdist suffix - customize test database name
• feature request, modifying sequences #84 - custom sequences - make it possible to run code after test database is created

Support having database fixtures in session, module, class scope:

• Do common db setup between tests once #105 - Do common db setup between tests once
• Support database access for "session" level fixtures. #243 - Support database access for "session" level fixtures

[pelme]

This is the issue which gathers some of the existing issues in one place. /cc @blueyed