Add support for Apache Cassandra DB

Install, configure and initialize Apache Cassandra v2.0 database for FrameworkBenchmarks.
This requires a user and group `tfb`, but none of the other database installations do. We should either automatically create this user/group and use it for all databases, or not use it here as we cannot be certain it exists. I know it's in the base readme to create them, but none of the other database install scripts use tfb