Change QueryResult to retain column value types

https://issues.cask.co/browse/CDAP-384
Since a Hive query result row only contains objects of primitive types, we define a new QueryResult.ObjectResult that holds the type and the primitive value.

Bamboo build: https://builds.cask.co/browse/CDAP-DUT114
After talking with Terence, we'll go with solution number 1) so that it's easier on any REST client to understand the format of a QueryResult.