Add language tabs and Python version to interactive part of quick-start

This is an addition of some stuff that was missed in https://issues.apache.org/jira/browse/SPARK-1567. I've also updated the doc to show submitting the Python application with spark-submit.

Author: Matei Zaharia <matei@databricks.com>

Closes #782 from mateiz/spark-1567-extra and squashes the following commits:

6f8f2aa [Matei Zaharia] tweaks
9ed9874 [Matei Zaharia] tweaks
ae67c3e [Matei Zaharia] tweak
b303ba3 [Matei Zaharia] tweak
1433a4d [Matei Zaharia] Add language tabs and Python version to interactive part of quick-start guide
(cherry picked from commit f10de042b8e86adf51b70bae2d8589a5cbf02935)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>