Use webpack for bundling JS libs and move Golang code related to Iframe generation there

javascript/src/viamapi-client.js

+const Penpal = require('penpal').default;
+
+function setupViamAPI(divId, methodsArg) {
+	const connection = Penpal.connectToChild({
+	  // URL of page to load into iframe.
+	  url: '{{urlArg}}',
+	  // Container to which the iframe should be appended.
+	  appendTo: document.getElementById(divId),
+	  // Methods parent is exposing to child
+	  methods: methodsArg
+	});
+
+	return connection.promise
+}
+
+window.setupViamAPI = setupViamAPI;
+