Added Contact Model (#34)

src/structures/PrivateContact.js

@@ -0,0 +1,13 @@
+'use strict';
+
+const Contact = require('./Contact');
+
+/**
+ * Represents a Private Contact on WhatsApp
+ * @extends {Contact}
+ */
+class PrivateContact extends Contact {
+
+}
+
+module.exports = PrivateContact;