plugin: Add subscriptions when processing the plugin manifest

Signed-off-by: Christian Decker <decker.christian@gmail.com>

lightningd/notification.c

@@ -0,0 +1,13 @@
+#include "lightningd/notification.h"
+#include <ccan/array_size/array_size.h>
+
+const char *notification_topics[] = {
+};
+
+bool notifications_have_topic(const char *topic)
+{
+	for (size_t i=0; ARRAY_SIZE(notification_topics); i++)
+		if (streq(topic, notification_topics[i]))
+			return true;
+	return false;
+}