Refactor to only have one function registerMenuCommand

When selected custom menu is removed, go to settings menu
Allow iframe in custom menu to use Scripting API
Return menu object when it is registered, can call remove function on it

maps/tests/Metadata/customMenu.js

@@ -0,0 +1,15 @@
+let menuIframeApi = undefined;
+
+WA.ui.registerMenuCommand('TO WA', () => {
+    WA.nav.openTab("https://workadventu.re/");
+})
+
+WA.ui.registerMenuCommand('TO WA BY IFRAME', {iframe: 'customIframeMenu.html'});
+
+WA.room.onEnterZone('iframeMenu', () => {
+    menuIframeApi = WA.ui.registerMenuCommand('IFRAME USE API', {iframe: 'customIframeMenuApi.html', allowApi: true});
+})
+
+WA.room.onLeaveZone('iframeMenu', () => {
+    menuIframeApi.remove();
+})