[xpcc-dev] Copy of SDLDisplay in gui example

Hi devs, you added the sdl_display.hpp to the example folder examples/linux/gui/sdl_display.hpp But the SDL display already existed as class of xpcc under #include <xpcc/architecture/platform/hosted/linux/display/sdl_display.hpp>. The additional functionality of this class should have been added there and then this class should be included in the example instead of copying the class files to the example folder. Best Regards, Thorsten