refactor!: finish parser migration

Finally! :)

This removes all code related to the old parser.

#65

lib/parser/classes/DownloadButton.js

@@ -0,0 +1,16 @@
+'use strict';
+
+const NavigationEndpoint = require('./NavigationEndpoint');
+
+class DownloadButton {
+  type = 'DownloadButton';
+
+  constructor(data) {
+    this.style = data.style;
+    this.size = data.size;
+    this.endpoint = new NavigationEndpoint(data.command);
+    this.target_id = data.targetId;
+  }
+}
+
+module.exports = DownloadButton;