discovery+routing: split 'routing' package on 'routing' and 'discovery'

In this commit the routing package was divided on two separete one,
this was done because 'routing' package start take too much responsibily
on themself, so with following commit:

Routing pacakge:
Enitites:
* channeldb.ChannelEdge
* channeldb.ChannelPolicy
* channeldb.NodeLightning

Responsibilities:
* send topology notification
* find payment paths
* send payment
* apply topology changes to the graph
* prune graph
* validate that funding point exist and corresponds to given one
* to be the source of topology data

Discovery package:
Entities:
* lnwire.AnnounceSignature
* lnwire.ChannelAnnouncement
* lnwire.NodeAnnouncement
* lnwire.ChannelUpdateAnnouncement

Responsibilities:
* validate announcement signatures
* sync topology with newly connected peers
* handle the premature annoucement
* redirect topology changes to the router susbsystem
* broadcast announcement to the rest of the network
* exchange channel announcement proofs

Before that moment all that was in the 'routing' which is quite big for
one subsystem.

split

routing/router_test.go

@@ -77,12 +77,6 @@ func createTestCtx(startingHeight uint32, testGraph ...string) (*testCtx, func()
 		Graph:    graph,
 		Chain:    chain,
 		Notifier: notifier,
-		Broadcast: func(_ *btcec.PublicKey, msg ...lnwire.Message) error {
-			return nil
-		},
-		SendMessages: func(_ *btcec.PublicKey, msg ...lnwire.Message) error {
-			return nil
-		},
 		SendToSwitch: func(_ *btcec.PublicKey,
 			_ *lnwire.UpdateAddHTLC) ([32]byte, error) {
 			return [32]byte{}, nil