Needed to import the types specifically, not the more general pyspark.sql

Author: Bill Chambers <wchambers@ischool.berkeley.edu>
Author: anabranch <wac.chambers@gmail.com>

Closes #5179 from anabranch/master and squashes the following commits:

8fa67bf [anabranch] Corrected SqlContext Import
603b080 [Bill Chambers] [DOCUMENTATION]Fixed Missing Type Import in Documentation