Change flow so home page is device select from where you can browse to overview

app.py

@@ -56,10 +56,15 @@ def devices():
     return render_template('devices.html', devices=devices)
 
 
-@app.route("/overview")
-def overview():
-    cadences = db.get_all_cadences()
-    last_cadence = cadences[-1]['rpm']
+@ app.route("/device/<device_id>")
+def device(device_id):
+    return render_template('device.html', device_id=device_id)
+
+
+@app.route("/overview/<device_id>")
+def overview(device_id):
+    cadences = db.get_all_cadences(device_id)
+    last_cadence = cadences[-1]['rpm'] if cadences else 0
 
     graph_data = generate_graph([c['logged_at'] for c in cadences[::2]], [
                                 ("RPM", [c['rpm'] for c in cadences[::2]])])