Add another missing header in MainWindow.c
Add another missing header in MainWindow.c

LarsAeschlimann/SuperTeacher,BFH-E1D-2015-2016/SuperTeacher,NicoHaui/SuperTeacher,LarsAeschlimann/SuperTeacher,NicoHaui/SuperTeacher,BFH-E1D-2015-2016/SuperTeacher,NicoHaui/SuperTeacher