[repository] 'session' argument is always given to type[_and_source]_from_eid, make it mandatory and simplify code accordingly

[repository] 'session' argument is always given to extid2eid, make it mandatory and simplify code accordingly

[web/data] Remove broken jquery-json plugin (closes #3590335) Conversion of Date() objects is somehow broken (don't know why beyond that it's due to jquery-json's monkeypatched Date.toJSON() method). Use the now-standard JSON.stringify() instead. http://caniuse.com/#feat=json says it's supported by all browsers, and even IE going back to version 8.

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]