Makie.jl: Documentation refactor

[SimonDanisch]

• [x] add MakieLayout documentation
• [ ] update StatsMakie tutorial to use AlgebraOfGraphics (@piever) and recipes that are no included by default
• [ ] move examples to Markdown files without the whole MakieGallery magic
• [ ] move usable code from MakieGallery to AbstractPlotting
• [x] move documentation files to AbstractPlotting so that documentation can be updated in one PR
• [ ] still host documentation in MakieGallery, so that the repository size doesn't explode... But all other functionality of MakieGallery should be stripped out
• [ ] have the starting page display outstanding examples
• [ ] export plots, wherever possible, as interactive HTML with WGLMakie
• [ ] update text, e.g. for Makie

[jkrumbiegel]

I don't think an AlgebraOfGraphics tutorial should live in the Makie docs. We should just prominently link to it so people are aware, with some nice images that get the gist across. But keeping docs updated across packages doesn't work (as we see by statsmakie still being in our docs even though it's old)