misc fixes:

- import from '@webrecorder/wabac' package for sw.js, though using github overrides for now
- replay: show loading spinner on beforeunload event in iframe
- embed: support passing basePageUrl param as part of extraConfig for custom top-level page

src/sw.js

@@ -11,11 +11,11 @@ if (self.registration) {
   staticData.set(prefix + "index.html", {type: "text/html", content: INDEX_HTML});
   //staticData.set(prefix + "ui.js", {type: "application/javascript", content: UI_JS});
 
-  const { SWReplay } = require('wabac/src/swmain');
+  const { SWReplay } = require('@webrecorder/wabac/src/swmain');
   self.sw = new SWReplay(staticData);
 
 } else if (self.postMessage) {
 // Inited as Web Worker
-  const { WorkerLoader } = require('wabac/src/loaders');
+  const { WorkerLoader } = require('@webrecorder/wabac/src/loaders');
   const loader = new WorkerLoader(self);
 }