Use /local instead of /scripts for tooling

[kasparsd]

Use /local as the canonical directory for storing everything that is not part of the actual plugin code such as tooling, Docker config, etc. We could end up with something like:

• /local/scripts for all Composer/Node scripts used for scaffolding and deploys.
• /local/public for mounting the root directory of the WordPress development environment.
• /local/docker for containing any Docker overrides and customizations.