Feature/1010 handle person accounts

# Warning
# Info
* This release fixes one problem with NPSP running correctly if Person Accounts are enabled.  It also provides an appropriate error message if you try to use Contact Merge with Person Accounts.  With this release, there are no outstanding issues that we are aware of when running NPSP in an instance that has had Person Accounts enabled.

# Issues
Fixes #1010
Fixes #1164