Add timestamp to converter status output

This is a simple change but has been a good sanity check for me when I started to question if the process had stopped on a large conversion.  It just adds a timestamp to each status update in the converter. 
Eg: 
  Instead of just Converting users (3333 - 3433) 
  it will show Converting users (3333 - 3433) June 18, 2014 4:50 pm

ALso respecting the WordPress timezone offsets