Assignment Time Zone localization

Provide dates relative to the timezone of the user.

All of the date and time ops in Assignments were refactored to use Java 8's time api and since its generally a widely accepted practice to store dates and time in UTC (this concept is the same in the xml doc).

However the Hibernate POJO's were using java.util.Date since Instant is not supported until Hibernate 5. After further experimenting dates were still not being stored in UTC. To address this added an Instant Hibernate Type to persist java.time.Instant. This is the best approach since it aligns with Hibernate 5 and will require the least amount of modification.