NOT FOR INCLUSION OGM-122 - Support Cassandra as Datastore

DO NOT MERGE 
This for discussion purposes only for Cassandra based integration into the Hibernate OGM, not for commit.

I known that this is a "horrible" pull request but this is just for discussion purpose because there is a lot of issue I don't know how to deal with.
A lot of work need to be done to have a "clean commit" (single?) and a clean code...

Presently, need :
- cassandra 1.2 running with native transport activated (start_native_transport: true) running locally
- a local build of the cassandra java-driver (https://github.com/datastax/java-driver) (version of the 01/14/2015)

Warning : cassandra builder should change soon and perhaps should we use PrepareStatement.

A lot of things do not run like :
- collection/type,
- manytoone,
- onetoone,
- id,
- conflict between long and bigint for simple test (simpleentity),
- not sure enumType works,
- lowercase issue,
- list, map, set,
... :'(

A lot of TODO too which need discussion.

I think that I missed something for the mapping between cassandra and hibernate types (CassandraTypeConverter).
Moreover I had to changed core test to make cassandra tests run...

To run test : 
mvn install -DskipTests
mvn test -Pcassandra -pl hibernate-ogm-cassandra