Test and fix "pickleability" of Binary objects which has been recently broken while some cubes rely on this (eg fastimport). Do some licensing/pep8 cleanup along the way. Closes #13385274

[server,bfss] fix storage migration when Bytes attributes is None (closes #13519541) When a Bytes attributes is None before the BFSS storage migration, the migration crashes. A Bytes attribute can be None, when the attribute is not required and there is no default value. In this case, the attributes should remained None after migration and no file is stored on the disk.

Let hg Ignore py.test's .cache directory And drop rule for .svn along the way.

[entity] Add a cw_related_rqlst method returning the RQL select node of cw_related method This is useful if one wants to modify the query before execution. A bit a PEP8 style fix in tests along the way. Related to #12306543.

[devtools] set .config in setUpClass instead of using a cache in a classproperty This is much clearer and avoid problem with py.test introspection that triggered creation and caching of the configuration before actual test execution. This caused pb in unittest_postgres.PostgresStatementTimeoutTC where configuration was built before module's setup, hence source configuration was missing information about where to find the pg cluster.

[devtools] Simplify test configuration's init Specify module's __file__ instead of apphome. __file__ is saved on the class as it will be used later (eg to find the proper pg cluster without relying on shared dictionnary modifications). This will require some tests update, but it should be less common in cubes than in cubicweb itself.

[web] Have the LoginController return 403 on failed auth (closes #11569950)

[devtools] Drop old init_test_database backward compat