Create Role, Status, and Priority enums

[timLP79]

Create the enum types needed by the entity layer:

• Role.java -- USER, AGENT, ADMIN
• TicketStatus.java -- OPEN, IN_PROGRESS, ON_HOLD, RESOLVED, CLOSED
• Priority.java -- LOW, MEDIUM, HIGH, URGENT

Package: com.absolutecode.ticketsystem.model

These are referenced by the User and Ticket entities and must be created before those entities.