Updates Cassandra example documentation.

fix some rt cleanup and failure edge cases

Updates the required properties to enable Cassandra as deep storage.
Also adds more information about how to create the required keystore,
and which properties files need to be modified to support Cassandra.
Also adds syntax highlighting to the provided example code.

Additionally, moves Cassandra Deep Storage documentation out into the
actual documentation hierarchy with appropriate linkage. A stub
README.md is left in the example directory to provide a useful landing
page for existing weblinks to the original documentation.

reduce object count overhead of column cache

fix missing queryGranularity in ArbitraryGranularitySpec