Add camptix_logged_out_message_after action

Sometimes the desired content can't be passed in to the camptix_private shortcode via the logged_out_message_after parameter because of limitations, like unfiltered HTML or nested shortcodes. This allows an arbitrary callback function to be hooked instead.
Logging warning instead of echoing

Echo'ing it was just for debugging but was accidentally committed
Merge remote-tracking branch 'origin/master'