[web] Only log exceptions in debug mode in Ajax controllers When we raise a RemoteCallFailed error (erroneously turned into a '500 Internal Server Error' response, but that's another business). In production environment, we do not want to log the exception in most cases where it's actually a client error. So only log the exception in debug mode.

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js