debinstall #8166 add a process to ensure directory/files permissions [deprecated]

Write the documentation about:

• the group capabilities
• the permissions on directory and files
• check owner and group before any action
• check if owner have group permission
• add owner config in debinstall ($USER by default) ?

And add simple tests (for now) to check this policy and try to manage files in an atomic way (i.e. changes file)