[PD-698] Added tags to xml, csv, and print-friendly export for PRM.

Before, tags were just empty, now they populate as a comma-separated list of values. 
Done. Was increasing the hits  by 1 for each contact record. Updated the commit to use prefetch_related which not only corrects this, but also reduces the original number of db hits (in master) from 54 to 53 WITH tags.