Handle the case were the Neutrino backend BTCd node is still
synchronising the blockchain as LND is not able to start syncing
until the BTCd node that it is connected to is fully synced.
Fetch the current block height from multiple block explorers early on in
the sync process. This ensures that we get the correct block height in
the case where our BTCd node is still mid way through syncing. Do this
in the main process rather than in the render process.
Determine the current block height directly from the lnd log output and
pass the data into the app as soon as we have it. Do not call out to
block explorers if we don't need to.
Tom Kirkpatrick
Jack Mallers
Ben Woosley