Added DrugEventTrigger class, created its hibernate mapping file and added required change sets in liquibase.xml
Added DAO for DrugEventTrigger class
Merge pull request #3 from mhawila/master

DAO and Implementaton for DrugEventTrigger metadata class
added drug event service layer methods that facilitates creation and consumption of drug events using event triggers
Finalized methods to generated drug events in DrugEvent service class and added unit tests
Implemented hibernate batch insert on DAO level, the API does not expose this to the user