[tests] Move 'anonymous_allowed' property from CubicWebServerTC to CubicWebTC
The effective set of the property on the config is now done later that before,
ie at the end of CubicWebTC.init_config instead of before.
It is believed not to have an impact on the test suites that uses
`anonymous_allowed`.
Related to #4002134
Schema of the data
------------------
First take a look at the data schema_ then try to remember that you are browsing
through a heap of data by applying stylesheets to the results of queries. This
site is not a content management system with items placed in folders. It is an
interface to a database which applies a view to retreived data.
.. _schema: schema