Network connectivity API

A home user wants to see a network connection status on Daedalus so that he/she knows the state of the network connection.

If the user receives a notification that they are in red or amber mode, Daedalus will give the user some helpful information on how to resolve common connectivity issues. There are three (at least) the following three distinct modes that the network can be operating in, each one has a red, green, amber status.

Initial block sync
----------------------
red receiving <1 blocks per 10s
amber receiving <10 blocks per 10s
green otherwise

Recovery
-------------
red receiving <1 block per 10s
amber otherwise
green (not applicable)

Block chain following
---------------------------
red it has been more that 200s since a slot indication was received.
amber it has been more than 60s since a slot indication was received.
green otherwise.

This assumes that the slot time remains 20 seconds, or at least that the average time
between production of new blocks is 20 seconds.