[cwctl] don't prompt for cube options in automatic mode Closes #3984223

[serverctl] fix default value for db-init config-level Otherwise cubicweb-ctl db-init --automatic complains that "--automatic and --config-level should not be used together" when they weren't. Closes #3984336

[web] Return useful error messages when exceptions arise in ajax controllers (closes #3932503) The call to super() in RemoteCallException passes 'reason' all the way to python's Exception.__init__() which is then stored in Exception.args. This way, CubicWebPublisher.ajax_error_handler() gets a useful error message when calling unicode(exc). The change to uilib is just to prepend the exception type name. Just a small improvement.

[test] Fix test breakage uncovered by previous changeset Now that Binary.__eq__ doesn't always return true, this test started failing. CWAttribute.defaultval is zpickled, and the description_format attribute is a String, meaning unicode, so adjust the expected test result.