Use venv activator instead of Python binary

visualizer.py

-#!/home/ograham/venv/bin/python3
+#!/usr/bin/env python3
 
-from dataclasses import make_dataclass
 import datetime
 from io import BytesIO
 import json
@@ -10,6 +9,11 @@ from types import SimpleNamespace
 from urllib.request import urlopen
 from wsgiref.handlers import CGIHandler
 
+# Activate the virtual env to get access to non-standard packages.
+activator = '/home/ograham/venv/bin/activate_this.py'
+exec(open(activator).read(), {'__file__': activator})
+
+from dataclasses import make_dataclass
 from flask import abort, Flask, g, jsonify, render_template, request, Response
 import matplotlib
 import matplotlib.pyplot as plt