Refactor KSMetaData

As part of CASSANDRA-9425 and a follow-up to CASSANDRA-9665, and a pre-requisite for new schema change protocol, this ticket will do the following

1. Make UTMetaData immutable (new Types class)
2. Refactor handling of the CFMetaData map in KSMetaData (new Tables class)
3. Factor out params into a separate class (KeyspaceParams)
4. Rename and move KSMetaData to schema.KeyspaceMetadata