Model: deduplicate list of legal parameters
Model: move node class override to class declaration...

... not class usage. This is less confusing.
node.t: test node class override
v2.064

  A small change for this release:

    * Version 2.062 added the possibility to override the Perl class
      implementing a configuration node by adding a class parameter in a
      place that is confusing. This release fix this bug: this optional
      override class is now declared at the top of a configuration class.