Add support for dropping tables

[hashbrowncipher]

This branch enables support for dropping tables. In addition do that, it:

• changes the capitalization of cfId to match the rest of the Cassandra codebase
• namespaces tables on-disk by cfId, so that tables which are dropped and re-created with the same name have different on-disk locations.

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[keshavdv]

Thanks for contributing! Do you mind rebasing -- we've since added optional RocksDB shards within the RocksDBCF so there are multiple instances where the table needs to be dropped. Can you also provide a more concrete migration path for users with existing non-UUID filepaths?