Resize image for android and iOS

Resize image script for iOS and Android by scale down from the best resolution image.

Use format

python resize_image.py (android/ios) destination source...

Android

hdpi 38%
mdpi 25%
xhdpi 50%
xxhdpi 75%
xxxhdpi 100%

iOS

@1x 33.33%
@2x 66.66%
@3x 100%