Fix scrapers to remove inline javascript in ZIM files

[mossroy]

As discussed in #789, browser extensions now enforce some CSP that block inline javascript. And it might happen in some other contexts, too.

Here is a list of affected scrapers that should be fixed (most critical first):

• [ ] https://github.com/openzim/gutenberg/issues/145 : main page unusable, other pages seem to work well
• [x] https://github.com/openzim/nautilus/issues/34 : main mage unusable, other pages seem to work well
• [ ] https://github.com/openzim/phet/issues/134 : main page unusable, other pages seem to work well
• [x] https://github.com/openzim/youtube/issues/154 : "only" affects the drop-down list of the home page, and loading of the webp-polyfill
• [ ] https://github.com/openzim/openedx/issues/168: a lot of inline javascript blocks + some "onclick" attributes
• [x] https://github.com/openzim/sotoki/issues/249 : several inline javascript blocks + some "onerror" attributes on some images
• [ ] https://github.com/openzim/mwoffliner/issues/1578 : minor. It seems to block webp-polyfill related code
• [x] https://github.com/openzim/wikihow/issues/108 : minor. It blocks some video-related javascript
• [x] https://github.com/openzim/ted/issues/128 : minor. It seems to block webp-polyfill related code
• [ ] https://github.com/openzim/kolibri2zim/issues/39 : minor. It seems to block webp-polyfill related code

NB: please tick the items in the list only when it has been tested with Kiwix-js with a public ZIM file