Cassandra 1.2

Hi Martin,

I have made the changes to make this plugin usable with lower version of cassandra 1.2/1.2.x, changes on a high level are captured below, also the changes passes all testcases. Request you to review and let me know your comments.

1. Datastax cassandra driver downgraded from 2.0.3 to 2.0.1(support cassandra version 1.2)
2. Cassandra-unit downgraded
3. Support added to create Keyspace with NeyworkTopologyStrategy also
4. BatchStatements replaces with CQL query batch wrapped in prepared statements
5. Parameterized Statements replaces with Prepared and Bound statements
6. Updated Readme.md

Thanks
Ratika
- Please do not use `println` but use `ActorLogging` trait instead. 
- Can you distinguish between a KeyspaceAlreadyExistsException and others? If yes, wouldn't it make sense to rethrow others?