Add support for mapping drugs to other terminologies - TRINK-4143

Added the DrugReferenceMap class and its hibernate mapping XML file. - TRUNK-4143

Updated the Drug.java and Drug.hbm.xml to include references to the new DrugReferenceMap class. - TRUNK-4143

Fixed issues in liquibase-schema-only.xml. - TRUNK-4143

Added addDrugReferenceMap method to Drug.java. Minor code fixes and improvements to Drug.java. - TRUNK-4143

Minor improvements to Drug.hbm.xml. Changed serialVersionUuid in DrugReferenceMap.java to conform to convention. - TRUNK-4143

Code and documentation improvemment to the addDrugReferenceMap method of the Drug.java class. - TRUNK-4143

Moved the changeset to create the drug_reference_map table from liquibase-schema-only.xml to liquibase-update-to-latest.xml. - TRUNK-4143

Follow up due to bad conflict resolution - TRUNK-4143