Make the docs embeddable

[kazk]

Replace outdated and unmaintained help tabs on Codewars.

When ?embedded=true, add html[data-embedded="true"] as early as possible, so we can style differently.

/* Hide navigation components when embedded. */
html[data-embedded="true"] {
  & .navbar,
  & .pagination-nav,
  & .footer,
  & div[class^="docSidebarContainer"],
  & div[class^="tableOfContents"] {
    display: none;
  }
}

(can also variant embedded and use embedded:hidden)

Also, allow overriding the theme with query parameter ?theme=dark|light to match the user's setting on Codewars. This should simply change html[data-theme].

[hobovsky]

BTW cold you provide places where "Help" tab is presented, what is its topic, and eventually what are the info tooltips there? Some of them might be outdated, but all of them present some kind of information which is needed to users, and it would be worthwhile to make sure that there's corresponding information in new docs. I think that many topics from help tabs are still not present in current docs, and there will be nothing to replace them with.

[kazk]

Kata editor:

Kumite editor:

We can add one in the trainer.

---

I can also show something to let users read the tutorial before creating a kata. Probably better to provide a link to open a new tab is better for this. There's only a brief tour of the kata editor at the moment.