Switch to python3 and scipy from slycot

Turns out we need python3 matplotlib to make scipy work well enough to
place the poles correctly for our systems.  Rather than do it piecemeal,
do it all at once.

This includes a python opencv upgrade too to support the new python, and
a matplotlib upgrade.

Change-Id: Ic7517b5ebbfdca9cc90ae6a61d86b474f2f21b29
diff --git a/y2018/control_loops/python/spline_generate.py b/y2018/control_loops/python/spline_generate.py
index 4376f37..cea3d7e 100644
--- a/y2018/control_loops/python/spline_generate.py
+++ b/y2018/control_loops/python/spline_generate.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python

+#!/usr/bin/python3

 import numpy as np

 import matplotlib.pyplot as plt

 from frc971.control_loops.python import drivetrain