Refine training pages

[iampava]

1. Clicking the logo should navigate to the main page (index)
2. Remove slides/events from header -> they're not pointing anywhere
3. Instead of slides/events add link to about page
4. All content should be in Romania (even about page)
5. Add new page where we'll add all people who've finished this challenge. This is where they will do a PR at the end with their name
6. Remove dummy "remove this lines" from AboutUs. Let's think of something else to remove, maybe we add a component in AboutUs and it's CSS is broken so we remove some of it
7. Add info in README (in En) -> saying these are practical challenges for practicing what we talked about in our training (link to training)
8. Add minimal SEO tags (see main repo and copy-paste frmo there)