SPARK-6988 : Fix documentation regarding DataFrames using the Java API

This patch includes :
 * adding how to use map after an sql query using javaRDD
 * fixing the first few java examples that were written in Scala

Thank you for your time,

Olivier.

Author: Olivier Girardot <o.girardot@lateral-thoughts.com>

Closes #5564 from ogirardot/branch-1.3 and squashes the following commits:

9f8d60e [Olivier Girardot] SPARK-6988 : Fix documentation regarding DataFrames using the Java API

(cherry picked from commit 6b528dc139da594ef2e651d84bd91fe0f738a39d)
Signed-off-by: Reynold Xin <rxin@databricks.com>