Move tuts from wiki to xonotic.org

I copied the markdown from the wiki and fixed links (except a vid in halogene's tut about laser + rampjumping that appears to have been removed, we should probably remove the link, unless someone has a copy).

I am not sure whether to keep headings so big. The FAQ page uses it's own css and other pages start with h3 but i kinda like how they separate the text. Only downside is that the title at the top of the page is smaller compared to them.

To make the items table in oktut have dark background, i had to remove the condition which only applied faq.css to the FAQ so now it applies to all pages that import header.html. I hope it doesn't break anything, but looks like cacs doesn't import header.html so it should be fine.

Oh, and i couldn't resist nuking another ancient FAQ about nexuiz which talks about xon in future tense.

Note to self: when merged, replace wiki pages with redirect links