Support for Cassandra NoSQL

Very basic but working support for Cassandra NoSQL 1.2.0. Requires
Cassandra JDBC connector 1.1.2 or later.
Supports:
- creation and using locking and log table
- changesets based on <sql> block with CQL
Merge branch 'master' of https://github.com/frederikcolardyn/liquibase into frederikcolardyn-master
Pulled cassandra support into separate repository