4 unit tests and added setters in class 'Parameter'

Unit tests for all classes in Transformer\Event that have methods.
Two setters added in Transformer\Template\Parameter
Unit test for Transformer\Template\Parameter
It doesn't break the test but may be confusing to anyone inferring the usage from the test: the 'element' that must be passed to the setElement method is of type DOMElement and not DOMDocument. This test may also break if a typehint were to be added on the setElement method