Remove requirement to declare simple modules

[fschopp]

At present simple modules need to be declared, so that they can then be invoked in dataflows. This is unnecessarily complicated: Composite modules, e.g., can be defined and used “ad-hoc”.

The CK object model needs to be changed accordingly: Collapse the ModuleDeclaration hierarchy, keeping the ‘template’ property from CompositeModuleDeclaration.