[devctl] properly generate i18n messsages for cubes that uses uicfg instances (closes #2811282)

[test/devctl] add a test case for i18ncube command

Protect against crash in the `relation_possible` predicate with ambiguous relations. It was still possible to get a KeyError when using relations that are ambiguous at both ends, like (Executable, version_of, Program) & (Version, version_of, Project). Closes #3010148.

[test] give a non-ambiguous order to sync_schema assertion (closes #3001959) Sorting by ordernum alone is unstable since several values have the same ordernum. ordernum + name should be stable.

Added tag cubicweb-version-3.17.3, cubicweb-debian-version-3.17.3-1, cubicweb-centos-version-3.17.3-1 for changeset 32b4d5314fd9

[test] typo

[schema,server] add a security debugging aid (closes #2920304) - Add a DGB_SEC debugging flag (to be used with set_debug/debugged). - Add a context manager (tunesecurity) to filter security assertions. Note: this does not address all read-security mecanisms.

[etwist] fix handling of multiple files per field html5 permits multiple files uploads, which can be expressed as:: <input type='file' multiple='multiple' /> This changeset avoids previous crash. Nothing is changed when a single file is uploaded (backward compat is thus preserved). When multiple files are uploaded for a single html input tag, the corresponding web request form key receives a list of tuples like [('filename-1', IStream1), ('filename-2', IStream2), ...]. closes #2847207.

[merge] start 3.18 development

[pkg] prepare 3.17.3