Relationships element in xPIL needs to be cleaned up

["Ram Kumar" <kumar.sydney@gmail.com>]

The Relationships element in xPIL uses Individual and Group relationship
categories.
This does not align with xPRL strategy where it does not matter whether it
is individual
or group as it is a type of party. Therefore, xPIL should be simplified to
have a Relationship
subelement that has the party's common details as defined.

Ram