Make it configurable: consistency level for schema version tracking statements

Currently it is hard coded to ALL, making it configurable gives us possibilities to work around some issues (in very sick use cases, I have to admit).

I have a quick implementation here: https://github.com/james-hu/cassandra-migration/pull/1/files
But probably the configuration should be on CassandraMigration rather than on KeyspaceConfiguration. Then we can pass it as an argument to the constructor of SchemaVersionDAO. That change seems to be a little bit structural. So I think I'd better let you take over.

Consistency level is configurable from Java (and command line as well?)

Consistency level of migrations scripts provided by the users.

Create a keyspace that can't satisfy the ConsistencyLevel.ALL, and try to make migration success by setting consistency level to QUORUM.