Refactoring & Service classes for the domain objects

* Removed the @GeneratedValue from the link, place,
media and tag model objects. The ids for these
objects are generated by a custom sequence generation
DB function

* The service classes serve to mediate interaction
between the presentation land data layers

* Added Log4J and mockito as dependencies to the 
project configuration file (pom.xml)

* Changed the name of the "getById" methods to 
"findById"

* Renamed AbstractHibernateDAOTest to AbstractSwiftRiverTest
as it's a base class for all test cases
Unit tests for the service classes

* For testability, each service class now has a 
mutator method for setting the DAO to be used
for transactions

* Added unit tests for the tag, channel, river, drop
river and bucket services. These tests primarily verify
that the service classes invoke the requisite DAO
methods