Extend CPD class to allow DBURI-derived Sources in maven-pmd-plugin 

As a DBURI may result in the addition of multiple Sources to CPD, in order to use DBURI within the calling CPDReport class, there must be a way of returning Sources or their associated signatures/paths to CPDReport. 

Additionally, the file suffix inferred from an object type is now different for Objecy Type and Package specifications and bodies.