Also swaps `PublicKey` for `NodeId` in `get_next_node_announcement`
and `InitSyncTracker` to avoid unnecessary deserialization that came
from changing `UnsignedNodeAnnouncement`.
Adds the macro `get_pubkey_from_node_id`
to parse `PublicKey`s back from `NodeId`s for signature
verification, as well as `make_funding_redeemscript_from_slices`
to avoid parsing back and forth between types.
