Hive improvements

A number of hive improvements:
* Ability to set performance options for hive queries
* Removed the unused hive conf from the sources.
* Ability to create external tables.

/cc @SamRoberts @tims 
The Map[String, String] is an escape hatch since not all the settings will be hive options. But in  most cases they will be which why one should use ConfVars to avoid mistakes.