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/embed.js

@@ -112,6 +112,7 @@ class Embed extends LitElement
         source: this.source,
         customColl: this.coll,
         config: this.config,
+        basePageUrl: window.location.href.split("#")[0],
         embed: this.embed,
       }).toString();