Adblock Support for Embeds (#308)

Fixes #307 

- Adds optional adblock support, via wabac.js (dependent on
webrecorder/wabac.js#167).
- For now, adblock enabled only for embeds via the `useAdblock`
attribute, and can be enabled per archived item.
- By default, adblock filter rules from
[EasyList](https://easylist.to/easylist/easylist.txt) are used, however,
a custom filter rules file can be used via `adblockRulesUrl` attribute
(default is ./adblock/adblock.gz)
- Added `fetch-adblock.sh` script to fetch latest easylist, filter out
`##` rules and compress to `./adblock/adblock.gz`
- Not yet possible to enable adblock for standalone browsing via
replayweb.page
- bumps version to 2.0.0-beta.3

src/appmain.ts

@@ -608,6 +608,11 @@ export class ReplayWebApp extends LitElement {
       this.loadInfo!.extraConfig.baseUrl = this.pageParams.get("basePageUrl");
     }
 
+    if (this.pageParams.get("adblockUrl")) {
+      this.loadInfo!.extraConfig = this.loadInfo!.extraConfig || {};
+      this.loadInfo!.extraConfig.adblockUrl = this.pageParams.get("adblockUrl");
+    }
+
     if (this.pageParams.get("customColl")) {
       this.loadInfo!.customColl = this.pageParams.get("customColl");
     }