Make tests startable again

This commit fixes some moved classes and deactivaes the PHP session
management while logging in a Django user. With this commit's changes
the tests module is just valid for Django again.
Tests: small doc update
Tests: move test data into fixtures directory
Tests: don't load test fixture by hand, let Django do it
Tests: represent test data as JSON

Django's test system can't load SQL fixtures.
Tests: add mock module dependency

This module is required for the testing system to build mock-ups for
Django models.
Tests: remove unneeded fixture from insertion test
Merge branch 'fix-test-infrastructure'