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/default_sets.go

@@ -71,4 +71,12 @@ var defaultSetDesc = setDesc{
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},
+	lnwire.ScidAliasOptional: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+	},
+	lnwire.ZeroConfOptional: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+	},
 }