[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.

[pyramid] Only expose 'cubicweb.bwcompat' setting for "all-in-one" configuration type The "pyramid" instance configuration does not work with "cubiwceb.bwcompat" mode (on purpose). Yet, having the setting exposed in development.ini file (generate by `cubicweb-ctl create --config pyramid <cube> <instance>` command) is misleading and we want to remove it. Thus, we only query this setting when cubicweb configuration is "all-in-one" and drop the setting line from templated development.ini file. If the option is found and True for any other configuration type, we issue a user warning (and ignore the option).