Document Back Office layout

@atomiix Would it be possible to write a documentation page about what the Back Office layout does?

It would be in PrestaShop 1.7 > Core Reference > Components > Back Office layout

Here is a draft

---
title: Back Office layout
menuTitle: Back Office layout
---

# The Back Office layout

Back Office controller return Back Office HTML pages.

Most of these pages Back Office page have a common HTML structure:
- a layout at the top
- a menu navigation bar on the left
- the page content at the center
- a collapsable right sidebar that contains documentation 

## Back Office Layout

TODO

I think you could write in there what you have reverse-engineered while working on rebuilding the Layout using Twig and Symfony (to get rid of Smarty legacy layout)