added XML funtionality to CourseCatalog, so that it can now instantiate
a CourseCatalog from a XML Element.
added method create().
fixed problem in StudentCatalog.
Modified Files:
src/java/de/fhworms/ztt/ox/campusdatarepository/CourseCatalog.java
src/java/de/fhworms/ztt/ox/campusdatarepository/StudentCatalog.java
src_test/java/unit/de/fhworms/ztt/ox/campusdatarepository/CourseCatalogTest.java
src_test/java/unit/de/fhworms/ztt/ox/campusdatarepository/StudentCatalogTest.java
