reconnect on interrupted connection to server

[megies]

I noticed that when the server goes offline and comes back online again we still do net get the data again. Maybe we could prompt a reconnect to server when we end up with a completely empty stream (i.e. no data on any station anymore).

But.. low priority as I think for most use cases restarting the plotter in a cronjob at night makes most sense, just wanted to mention here.