Import Members - add logic to populate the Reminder Date column based on end date and membership type settings

There is a patch for this - which hopefully handles it by calculating the Reminder Date based on the incoming End Date - at: http://forum.civicrm.org/index.php/topic,5610.msg24920.html#msg24920

We should also allow users to access this field via Batch Update from Profile, and allow them to map input data to this column during Member Import.