This issue employs logic similar to the bash launcher (pyspark) to check
if IPTYHON=1, and if so launch ipython with options in IPYTHON_OPTS.
This fix assumes that ipython is available in the system Path, and can
be invoked with a plain "ipython" command.

Author: Michael Griffiths <msjgriffiths@gmail.com>

Closes #2910 from msjgriffiths/pyspark-windows and squashes the following commits:

ef34678 [Michael Griffiths] Change build message to comply with [SPARK-3775]
361e3d8 [Michael Griffiths] [SPARK-4065] Add check for IPython on Windows
9ce72d1 [Michael Griffiths] [SPARK-4065] Add check for IPython on Windows