Treat Wombat as a dependency

[rgaudin]

Wombat.js should not be included in our repo. It should be downloaded from a release instead.

webrecorder/wombat#128 tracks our patch ; if this can't make it upstream, we should patch the downloaded version.

[Jaifroid]

Presumably this is for v2.0. You're probably aware that wombat.js and wombat worker are included in sw.js as two very long minified strings. This may be irrelevant going forward as we are ditching the Service Worker, but it does bloat sw.js unnecessarily IMO, especially as we currently include wombat.js in every ZIM as well.

(Having said that, my implementation in the Browser Extension extracts and uses the version included in sw.js, so in the unlikely event that this were to be changed, I'd need to know.)

[mgautierfr]

Last version of wombat (https://github.com/webrecorder/wombat/releases/tag/v3.7.0) contains our fix.
So we are good to use (and download) the release instead of embed it in our repo.

[kelson42]

Fixed by #146