lnwallet: properly populate the signDesc within UnilateralCloseSummary
lnwallet: properly populate the signDesc within UnilateralCloseSummary

This commit modifies the closeObserver code to populate the signDesc in
the case we have a non-trimmed balance. Additionally, we now also add a
*wire.OutPoint field to the struct in order to allow receivers of the
message to construct a witness that can spend the newly created output
to their wallet.

AndrewSamokhvalov/lnd,ddustin/lnd,LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd,ddustin/lnd,aakselrod/lnd,AndrewSamokhvalov/lnd