cmd/lncli: move commands and export

We want to export some of our CLI code to re-use in other projects. But
in Golang you cannot import code from a `main` package.
So we need to move the actual code into its own package and only have
the `func main()` in the `main` package.

cmd/commands/routerrpc.go

@@ -0,0 +1,17 @@
+package commands
+
+import "github.com/urfave/cli"
+
+// routerCommands returns a list of routerrpc commands.
+func routerCommands() []cli.Command {
+	return []cli.Command{
+		queryMissionControlCommand,
+		importMissionControlCommand,
+		queryProbCommand,
+		resetMissionControlCommand,
+		buildRouteCommand,
+		getCfgCommand,
+		setCfgCommand,
+		updateChanStatusCommand,
+	}
+}