Titan with Cassandra CQL

This is the current implementation of CQL support. There are failing unit tests, mostly caused by latest changes in Titan core, that I did not yet implemented.

Some refactoring is still required.

I will continue to push my work to this pull request. 

Any comments/suggestions are welcome. 

I have tried to use same data model, replacing wide rows with cql equivalent, that is table with compound primary key.