Improved data-model and related tests.

Signed-off-by: Paulo Pires <pjpires@gmail.com>
Updated Cassandra dependency to 1.2.4.

Signed-off-by: Paulo Pires <pjpires@gmail.com>
Added maven-clean-plugin execution instructions.

Signed-off-by: Paulo Pires <pjpires@gmail.com>