Update CMakeLists.txt
Format source code with Astyle
Gui/ScrollArea::getChildWidget(): Return something

Clang can generate SIGILL if a function that should return something
does not return anything, making the program crash
Map/TileMap.cpp: Fix signed/unsigned comparison warnings
Map/Tilemap: Fix shadowed declaration
Map/Tilemap::display(): Reduce scope of xmin, ymin, xmax, ymax
Gui/ScrollArea::setChildWidget(Widget*): Mark parameter as unused to avoid warning