add relay logging (#1263)

This PR adds relay logging to the RelayDetailView.

Features:

* list of events, most recent at the top

* shows changes to RelayConnection's state

* shows changes to network state

* RelayDetailView updates live as lines are added to the log

* logs persisted to disk for later investigation

* line limit prevents unbounded file growth

Here's how it looks when resuming after having the app in the background for a while and the relays need to reconnect: