Localize test data

[lukasrad02]

The database seeds ("test data") that can currently be generated using python manage.py create_test_data only create pages in the German page tree, but using English page titles. I'd propose to

• change the current data to use German titles, slugs etc (to avoid confusion by pages from the test data not being visible while being in the English page tree)
• add translations of these pages to the test data set to encourage and make it easier to test new features in the translation and not only in the German version