Update cassandra driver to 2.1.0

The 2.0.0-rc2 driver has a bug
(https://datastax-oss.atlassian.net/browse/JAVA-254) which gets
triggered when querying through presto.  An exception occurs because the
driver attempts to query a table that no longer exists, and fails.

Cassandra 2.1.0 is the current stable release, so it's probably time to
catch up.  The hector library has been removed and replaced, because it
didn't seem to work correctly with C* 2.1, and the project doesn't
appear to be very active.
Fix formatting
Fix typo in JMX connector documentation
Allow reading/writing sequences of pages with mixed block types

The current implementation causes problems when a single remote request
gets multiple pages that have different encodings for a given column. This
could happen, for example, if the stream is the result of a union of
subqueries or tables that produce different types of blocks for any given column.

The reason is that the identifier for the block encodings is written once per request
based on the encodings of the first page. This fix changes the wire serialization format
to include the block encodings for each page in the response.
Set context class loader when creating ORC writer

The ORC memory manager ends up loading VersionInfo which loads classes
from the context class loader. The tests now set an empty class loader
to verify that it uses the correct class loader.
Add favicon for UI
Add scheduled flag to query info
Only show progress in UI when scheduled
Improve error message for scalar subqueries in groupby
Remove duplicate helper functions in test
Fix formatting for tests
Render byte arrays in the CLI as a hex dump
Improve error message for window functions without an OVER clause
Fix static import warning in PrestoS3FileSystem
Configure MaxRetryTime in PrestoS3FileSystem
Update 0.80 release notes
Add 0.80 release notes
Enable optimized readers by default
Disable new RcFileReader until GC issues are resolved
Fix cassandra timestamp type (from bigint to timestamp)