added toString function
added functions to help testing, getClasses and getAssociations. Also added possibility to get the XML-Document instead of exporting it to a file. This way we can test without having to read files and we can scan the Document-tree instead of the direct xml
Changed testing from file to Document. Now we check if classes and associations exist instead of checking if the xml is 100% the same. This way we can make changes to the xml without letting the tests fail.
Changed magic literals so we can modify the xml-standard later. Also moved the createElement-functions to this file.