Mailings.tpl tries to load mailing.json that doesn't exist.

Created by: rocxa

var data = {crmSQL json="mailing"}; // this is looking for a non existent file. Should be 'mailings'

However, with civicrm 4.7 the json formatted sql snippets don't load up so we had to create mailings.sql (with just the sql part from mailing.json in it) instead to get the mailings visualisations to work.