Added the remaining classes and a ObjectTimestamp to track object modifications.

opp/core/src/main/java/OPStaff.java

opp/core/src/main/java/ObjectModification.java

opp/core/src/main/java/ObjectTimestamp.java

opp/core/src/main/java/Operation.java

opp/core/src/main/java/OperationTeam.java

opp/core/src/main/java/Patient.java

opp/core/src/main/java/PreparationNote.java

opp/core/src/main/java/Role.java

opp/core/src/main/java/Room.java

opp/jdbc-repo-impl/src/main/java/JDBCRepository.java

opp/jdbc-repo-impl/src/test/java/Tests.java