Add minimal gameplay

icons/button_start.svg

icons/difficulty_easy.svg

icons/difficulty_hard.svg

icons/difficulty_medium.svg

icons/difficulty_nightmare.svg

icons/game_fail.svg

icons/game_win.svg

icons/size_10x10.svg

icons/size_15x15.svg

icons/size_20x20.svg

icons/skins/default/0.svg

icons/skins/default/1.svg

icons/skins/default/2.svg

icons/skins/default/3.svg

icons/skins/default/4.svg

icons/skins/default/5.svg

icons/skins/default/6.svg

icons/skins/default/7.svg

icons/skins/default/8.svg

icons/skins/default/mine.svg