Rework yaml layouts

This MR is about reworking the way the layout yaml files are parsed in client side in order to make it a bit more flexible.

The yaml nodes are typed. Each type is handled by a dedicated React component from yaml-layout.

The yaml-layout/utils.jsx provides shared API to register new node type, and render sub tree.

The main layout is handled by Layout.jsx

• It registers the available node types

Two new layouts was added:

• form, to create title->widget layout
• grid, based on CSS grid