CRM-15943 - Move replyTo option from $config to a setting.

CRM-15943 - Move replyTo option from $config to a setting.

Note: I tried using the prefetch/config_only options, but they didn't seem
to work.  Through some kind of magic, however, the setting data seems to
migrate from $config over to settings system (if prefetch and config_only
are *disabled*).