"Last Seen" column for disconnected Canopy SUs

One piece of information that I think would be useful to have on the session status page for Canopy AP’s would be the amount of time since the SU disconnected from that AP. I think it would be useful at a glance for troubleshooting, rather than having to dig into our snmp monitoring or cnmaestro.

This was implemented in R15.2 on the 450 platform!

It's called Session Downtime: