D-Net

#913 changing DocumentContentUrl#contentSize field type from string to int

#913 introducing DocumentContentUrl#contentSize field, handling it properly in all PIG transformers

#840 moving IdentifierMapping from importer to common package

#840 renaming DeduplicationMapping to more generic IdentifierMapping

introducing PmidMapping schema

updating countryCode comment to: country ISO 3166-1 alpha-2 uppercased code

Adding info on where to find types of citations produced by PMC citation ingestmodule

fixing comment

introducing address field

adding new countryCode field to affiliation