Add missing relation types items in schema global variables Some of these global variables are used, in particular, to control schema views (web/views/schema.py). While they are currently not properly documented (see #3360868), their definition are currently incomplete (e.g. one could reasonably expect to find ``cw_schema`` in ``SYSTEM_RTYPES``). Closes #3486114.

[web] return 403 for Unauthorized, not 401 401 is reserved to HTTP authentication. Just because it's also called "unauthorized" doesn't mean it's the same as cubicweb's Unauthorized exception. Closes #3648809.

[test] update unittest_repoapi to 3.19 api (sic) [jcr: while at it, fix typos and add missing __main__ section]

[test] update unittest_utils to 3.19 api

[test] update unittest_rset to 3.19 api [jcr: use self.admin_access instead of creating a new one each time]

[test] update unittest_rqlrewrite to 3.19 api

[test] update unittest_req to 3.19 api [jcr: use self.admin_access instead of creating a new one each time]

[test] update unittest_predicates to 3.19 api [jcr: use self.admin_access instead of creating a new one each time]

[web/test] port unittest_reledit to RepoAccess API

[web/test] port unittest_magicsearch to RepoAccess API request created in setUp makes context manager usage painful, so create a context manager to do the setup for each test class.

[web/test] use real_error_handling context manager instead of open-coding it

[web/test] port unittest_idownloadable to RepoAccess API

[web/test] remove useless calls to self.request() from CORS tests

[web/test] port unittest_formfields to RepoAccess API

[web/test] port unittest_form to RepoAccess API