[SQL] Break hiveOperators.scala into multiple files.

The single file was getting very long (500+ loc).

Author: Reynold Xin <rxin@apache.org>

Closes #1166 from rxin/hiveOperators and squashes the following commits:

5b43068 [Reynold Xin] [SQL] Break hiveOperators.scala into multiple files.

(cherry picked from commit ec935abce13b60f353236566da149c0c87bb1002)
Signed-off-by: Michael Armbrust <michael@databricks.com>