Move `a4paper` option to class options

Currently something is going wrong with the template when used on arxiv. Regardless of the a4paper option in the internal adaption of the KOMA Script class, the page layout is turned into US-Letter on arxiv. Adding a4paper as an option to the documentclass fixes this problem. Maybe something like \PassOptionsToPackage{a4paper}{geometry} could also do the trick, assuming that wrong detection of the paper format in geometry is the only problem.