Merge branch '31-keep-first-skin-only' into 'master'

android/gradle.properties

assets/icons/skin_numbers.png

assets/icons/skin_retro.png

assets/icons/skin_symbols.png

assets/skins/numbers_0.png

assets/skins/numbers_1.png

assets/skins/numbers_2.png

assets/skins/numbers_3.png

assets/skins/numbers_4.png

assets/skins/numbers_5.png

assets/skins/numbers_6.png

assets/skins/numbers_7.png

assets/skins/numbers_8.png

assets/skins/retro_0.png

assets/skins/retro_1.png

assets/skins/retro_2.png

assets/skins/retro_3.png

assets/skins/retro_4.png

assets/skins/retro_5.png

assets/skins/retro_6.png