Add node id to remaining `RoutingMessageHandler::handle_` methods

Add node id to remaining `RoutingMessageHandler::handle_` methods

Previously, some `RoutingMessageHandler::handle_` methods (in particular
the ones handling node and channel announcements, as well as channel
updates, omitted the `their_node_id` argument. This didn't allow
implementors to discern *who* sent a particular method.

Here, we add `their_node_id: Option<&PublicKey>` to have them learn who
sent a message, and set `None` if our own node it the originator of a
broadcast operation.