lnwire: separate ChannelID into a distinct struct, add tests

This commit separates out the ChannelID into a new file, with
additional helper methods for conversion and formatting. With this
commit, the struct is now more general purpose and can be used in the
new routing package, database, and other related sub-systems.

lnwire/channel_id_test.go

@@ -0,0 +1,39 @@
+package lnwire
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/davecgh/go-spew/spew"
+)
+
+func TestChannelIDEncoding(t *testing.T) {
+	var testCases = []ChannelID{
+		{
+			BlockHeight: (1 << 24) - 1,
+			TxIndex:     (1 << 24) - 1,
+			TxPosition:  (1 << 16) - 1,
+		},
+		{
+			BlockHeight: 2304934,
+			TxIndex:     2345,
+			TxPosition:  5,
+		},
+		{
+			BlockHeight: 9304934,
+			TxIndex:     2345,
+			TxPosition:  5233,
+		},
+	}
+
+	for _, testCase := range testCases {
+		chanInt := testCase.ToUint64()
+
+		newChanID := NewChanIDFromInt(chanInt)
+
+		if !reflect.DeepEqual(testCase, newChanID) {
+			t.Fatalf("chan ID's don't match: expected %v got %v",
+				spew.Sdump(testCase), spew.Sdump(newChanID))
+		}
+	}
+}