Declarative configuration documentation for version 6

• Basicaly, the lua configuration replaced by YAML snipets. This means that the new documentation is in the same location as in the previous version.
• The text is edited to make sense with the declarative configuration.
• Some parts have been deleted completely as they are not relevant for declarative configuration or are handled in background (lua scripting, modules loading, ...)
• All old Lua documentation is moved to Lua scripting subsection.