This commit bumps the compile time dependency of lnd and lndclient to
the 0.16.x branch. This makes the code forward compatible but does not
yet change anything with respect to the minimum required version the
user needs to run.
When traders create channels as part of a batch, the auctioneer provides
a guarantee to punish any traders who violate the lifetime of a channel
(also known as their maturity height). In order for the auctioneer to
carry out this duty, it'll need to retrieve a set of channel keys from
each trader to detect, in the event of a lifetime violation, who the
responsible trader was. This channel info is retrieved by the traders
from their encrypted SCBs.
