Reorganize repository: split ONBUILD images, rename to dooba, separate scaffolding

[yajo]

Current code layout is a bit messy, and it's going to get fixed soon. Things that will happen:

• This repository will be renamed to tecnativa/doodba.
• Main docker image will stop receiving updates.
• Main docker image will be renamed to tecnativa/doodba, to have a more solid branding.
• In that new image, tags [8-11].0 will be just a bare image with all Odoo dependencies.
• Also in that new image, tags [8-11].0-onbuild will perform all the magic to combine them with official scaffolding.
• Scaffolding will be split to its own repository https://github.com/Tecnativa/doodba-scaffolding, and use those new images.

[yajo]

Done. Docs updated in repo. Summarizing:

• Instead of using tecnativa/odoo-base:11.0 image in your scaffolding, use tecnativa/doodba:11.0-onbuild. The same for all versions.
• Instead of cloning scaffolding from git clone -b scaffolding https://github.com/Tecnativa/docker-odoo-base.git, use the new dedicated repo with git clone https://github.com/Tecnativa/doodba-scaffolding.git
• If you have any odoo-based docker project, you can use the tecnativa/doodba:11.0 (without -onbuild, same for all versions) as a base for that. Let's reuse!

You'll have to wait until builds are finished in the Docker Hub, though.