Move splashs to private and optmize size

mobile-config.js

private/splash/android-land-hdpi.png

private/splash/android-land-ldpi.png

private/splash/android-land-mdpi.png

private/splash/android-land-xhdpi.png

private/splash/android-land-xxhdpi.png

private/splash/android-land-xxxhdpi.png

private/splash/android-port-hdpi.png

private/splash/android-port-ldpi.png

private/splash/android-port-mdpi.png

private/splash/android-port-xhdpi.png

private/splash/android-port-xxhdpi.png

private/splash/android-port-xxxhdpi.png

private/splash/android_base.png

private/splash/ipad_landscape.png

private/splash/ipad_landscape@2x.png

private/splash/ipad_portrait.png

private/splash/ipad_portrait@2x.png

private/splash/iphone.png

private/splash/iphone5.png