Reorganize project

[rshym]

• remove self-reference from the yaml;
• move yocto layers into the dedicated directory;
• add .gitignore with build products;
• remove 'Fetching' chapter from the README as outdated.

[rshym]

Comments are addressed. The commit message is provided with additional explanations.

[rshym]

Rb is added. Tested by the build moulin prod-devel-rcar.yaml --MACHINE h3ulcb-4x2g --GRAPHICS binaries --ENABLE_DOMU yes. Ready to be merged.