Throw sensible error for wrong mission choice

Create Mission XML aboarded abnormally (e.g. when wrong mission was chosen). Fixed this

added modulecreate_mission_xml typebug labels

requested review from @kbistreck

assigned to @gPauls-TUHH

enabled an automatic merge when all merge checks for 385425c7 pass

The error messages look a bit chaotic (and the segmentation fault in the end is weird) but the user can understand the problem...if you are bored you can try to reorder it, otherwise merge :D

canceled the automatic merge

approved this merge request

mentioned in commit 21276b97

merged

mentioned in issue #54 (closed)