Shorten duration of ssh connection?

[sverhoeven]

Now we create a ssh connection during startup of the app and close it when the app closes. It seems wasteful to have a open ssh connection when the app is not being used.

Having shorter duration will make the time it takes to connect more obvious. We should check whether connecting in each url router handler is still performant enough. This will make the app context much simpler.

Issue derived from #16 (comment) comment