[cwconfig] Remove useless 'ui-cube' configuration option (closes #3728904) The mechanism introduced could never actually be used as it brings dependency loops to the cube graph. Just get rid of it. This reverts commit 4032499c701e.

[test] Use RepoAccess.shell() in unittest_predicates

[devtools] add 'shell' method to RepoAccess, deprecate CubicWebTC's Lets us control the connection's lifetime.

[repo] make extid2eid work with either a session or a connection The only place it should matter is for restoring pending_operations in case of failure. Which is not exercised by the test suite. Here be dragons.

[repository] extid2eid's 'commit' argument no more necessary This removes the need for creating an internal session.

[repository] complete argument is no more needed since we have no more 'true' multisource. It is always false.

[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.