UI Docs update

[aspiringLich]

This is to go along with the pr space-wizards/space-station-14#29903.

In this PR I:

• Mark the previous UI guide as outdated (don't delete for now, because downstream forks or something)
• Move the "documentation" for the Robust.Client controls into their own doc (for some poor sod who wants to add more) (that poor sod may be me)
• "UI and You" may be the greatest piece of literature to date, and covers the new styling system very well, and makes a half-hearted attempt at explaining C# UI code (someone who knows this better please fix)
• "UI Cookbook" so people know things exist, and then they like, use them, I guess.