Support UDF and Aggregate Function Schema Meta

Changes: https://github.com/datastax/python-driver/pull/268.
These include some integration tests. TBD: Cluster refresh entry points, including new parameter validation.

These changes assume the latest patch in https://issues.apache.org/jira/browse/CASSANDRA-8374

I encountered a few possible server-side bugs along the way. I have an email out to the author following up.

Added comments to the PR. +1 Only one of the comment might be an error.

Addressed comments on PR. Thanks for the review.

Assigning to for review of tests included in original PR.

Looked through all the changes and tests. I added some documentation for existing tests. Looks like we have some good coverage here.

Assigning to Adam for PR.