Gather network statistics

[lgrahl]

It would be helpful to have more metrics for the support team. We can measure...

• the type of connection (relayed, direct, on mobile network type),
• the RTT,
• the message/ack time for each ARP message that does have promises,
• transport buffer fill status,
• throughput (might need to be tied to message/ack).

We can also display this information to the user, perhaps even in form of a graph.

Supersedes #13.