lnwallet/btcwallet: update implementation to account for recent API changes
lnwallet/btcwallet: update implementation to account for recent API changes

The new version of the internal core of btcwallet now uses KeyScopes
rather than address types to derive particular addresses. As a result,
in this commit, we update our API usage to ensure that proper addresses
are still derived.

LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd