lnwallet: add a  MaturityDelay field to UnilateralCloseSummary
lnwallet: add a  MaturityDelay field to UnilateralCloseSummary

This commit adds a new field: MaturityDelay, to the
UnilateralCloseSummary struct. This new field will be required, in an
upcoming update as it’s needed in order to properly sweep the
second-level HTLC outputs after MaturityDelay blocks has passed since
confirmation.

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