created new Visitor for deserialization of advanced XML files/strings
all parsing will depend on the DOM classes of php instead of SimpleXMLElement
created a own Exception for this handling,
more stuff planed

addes some annotations/comments where i get to do it, for easier workaround and
reading

Signed-off-by: Maximilian Berghoff <Maximilian.Berghoff@onit-gmbh.de>