lnwire+feature: new zero-conf, scid-alias feature bit + chantypes

This defines the zero-conf feature bit, the scid-alias feature bit,
the zero-conf channel type, and the scid-alias channel type. It also
defines the dependency "tree" that exists for the feature bits.

The scid-alias feature bit signals that the node requires an alias
short channel id to be sent in funding_locked. The scid-alias channel
type requires that the channel is private, in addition to some other
forwarding-related privacy measures.

feature/deps.go

@@ -72,6 +72,12 @@ var deps = depDesc{
 	lnwire.KeysendOptional: {
 		lnwire.TLVOnionPayloadOptional: {},
 	},
+	lnwire.ScidAliasOptional: {
+		lnwire.ExplicitChannelTypeOptional: {},
+	},
+	lnwire.ZeroConfOptional: {
+		lnwire.ScidAliasOptional: {},
+	},
 }
 
 // ValidateDeps asserts that a feature vector sets all features and their