The Validation class in its current implementation
a) adds all available validations to the _handler dict and cannot be initialized with a different set of validations. Modifying the list of registered handlers in one instance leads to the same modification in all other instances.
b) runs a full validation with the odml object it is initialized.
c) cannot re-run a full validation, a new instance of the Validation class and the object has to be created to run another full validation.

The Validator class should be refactored

• to enable instantiating Validation objects with individual sets of validation handlers which includes providing a method that includes adding validation handlers to a class instance and not only to the class itself.
• to allow a Validation to be instantiated without automatically running a full validation on init.
• to include a method that allows to re-run a full validation on the Validation instances object.