XLSParser: Id within submission type name is ignored

Currently the id at the end of the submission type name is stripped when using the xls converter.

task_head_re = re.compile(r'^Quellcode Frage (?P<title>.*?) ?(\d{8})?$')

It is however, part of the name specified by the lecturer and should be included in the output (this is also the behaviour of the qti parser).