added support for variables in properties (based on @esromneb's patch)
replaced Evaluator#getValue by IInstantiator#evaluate
Indeed, the evaluator must take into account that variables may have
their values overridden at instantiation. Now it does.
evaluator now evaluates the value of mapped variables
instantiation context now solves the values of variables
renamed CExpression to CxExpression
simplified model, ValueList => ExpressionList (extends CxExpression)
renamed CType to CxType
corrected evaluator in case of functions