Add an option for the visualisation web interface to auto-refresh

Change-Id: Iee39e5c221a57d7e418a236b546cd790cd3902b3
diff --git a/visualisation/visualisation.py b/visualisation/visualisation.py
index 72c5ee7..164db5f 100644
--- a/visualisation/visualisation.py
+++ b/visualisation/visualisation.py
@@ -94,11 +94,14 @@
         self.send_response(200)
         self.wfile.write('Content-type: text/html\r\n')
         self.end_headers()
+        config = self.server.state.config.visualisation
         page = []
         page.append('<html>')
         page.append('<head>')
         page.append('<TITLE>VLANd visualisation</TITLE>')
         page.append('<link rel="stylesheet" type="text/css" href="style.css">')
+        if config.refresh and config.refresh > 0:
+            page.append('<meta http-equiv="refresh" content="%d">' % config.refresh)
         page.append('</HEAD>')
         page.append('<body>')
         switches = self.server.state.db.all_switches()