This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules
In this commit, we add a series of functions that will allow users to
recover existing channel backups. We do this using two primary
interfaces: the ChannelRestorer, and the PeerConnector. The first
interfaces allows us to abstract away the details w.r.t exactly how a
channel is restored. Instead, we simply expect that the channel backup
will be inserted as a sort of "channel shell" which contains only the
data required to initiate the data loss protection protocol. The second
interface is how we instruct the Lightning node to connect out to the
channel peer given its known addresses.
