Multiple minor updates.
+ Package names are changed to com.example.chirp.
+ Model objects now have a default constructor and setters so they can
safely unmarshal using JAX-B.
+ Post is now Chirp
+ UserRepository no longer saves state.  Instead Server.java calls
prepopulate().
+ Shared configuration is now in Server.chirpApplicationConfig().
+ Within Server.chirpApplicationConfig() package scanning for
resources/providers is commented out, and replaced with a JAX-RS
compatible ChirpApplication.
+ HelloResource now uses /greeting (I liked how you did that.)
+ EntityException's have a few minor upgrades.