Improve game architecture

android/app/build.gradle

android/gradle.properties

assets/icons/colors_5.png

assets/icons/colors_6.png

assets/icons/colors_7.png

assets/icons/colors_8.png

assets/icons/level_easy.png

assets/icons/level_hard.png

assets/icons/level_medium.png

assets/icons/level_nightmare.png

assets/icons/size_extra.png

assets/icons/size_large.png

assets/icons/size_medium.png

assets/icons/size_small.png

assets/icons/skin_default.png

assets/skins/default_0.png

assets/skins/default_1.png

assets/skins/default_2.png

assets/skins/default_3.png

assets/skins/default_4.png