Set lightning invoice id, rhash and msatoshi as direct metadata fields

So that they're easier to access in the admin dashboard and in CSV exports.

Closes #13.

Author: shesek

woocommerce-gateway-lightning.php

@@ -208,6 +208,10 @@ public function register_gateway($methods) {
 
       protected function update_invoice($order, $invoice) {
         $order->update_meta_data('_lightning_invoice', $invoice);
+        $order->update_meta_data('lightning_id', $invoice->id);
+        $order->update_meta_data('lightning_rhash', $invoice->rhash);
+        $order->update_meta_data('lightning_msatoshi', $invoice->msatoshi);
+        $order->update_meta_data('lightning_msatoshi_received', $invoice->msatoshi_received);
         $order->save_meta_data();
 
         if ($invoice->status == 'paid' && $order->needs_payment()) {