[test] Inline _test_available_cubes() method in cwconfig tests Improves readability.

[DX] adding error messages to {ResultSet,ActionsRegistry}.possible_actions Try to make it more accessible, when we first encountered these errors it it didn't made any sense to us.

[server/querier] remove useless indirection QuerierHelper._annotate

[server] remove useless indirection ExecutionPlan.sqlannotate Simpler is better. Use directly ExecutionPlan.querier.sqlgen_annotate.

[web] removed unused imports in basecomponents

[test] Depends on psycopg2-binary Avoids the following warning: The psycopg2 wheel package will be renamed from release 2.8; in order to keep installing from binary please use "pip install psycopg2-binary" instead. For details see: <http://initd.org/psycopg/docs/install.html#binary-install-from-pypi

[doc/changelog] the removal of next_tabindex produce an error not in the changelog When one tried to migrate to 3.25, the error "class X initialization doesn't have a settabindex argument" can happen but the word "settabindex" is not present in the changelog which makes it hard to find to which modification this error is related.

Merge with branch 3.26

[py3.7,test] Use cubicweb-file >= 2.2.2 This includes changeset aa4a3a3d0c18 fixing import of os.errno.

[flake8] Fix errors in cubicweb/ext/test/unittest_rest.py