launcher/notification icon的尺寸标准

来自stackoverflow：

标准：

LDPI should be 36 x 36.

MDPI should be 48 x 48.

TVDPI should be 64 x 64.

HDPI should be 72 x 72.

XHDPI should be 96 x 96.

XXHDPI should be 144 x 144.

XXXHDPI should be 192 x 192.

WEB 512 x 512

计算方式：

MDPI at 48 x 48

LDPI is MDPI x 0.75.

TVDPI is MDPI x 1.33.

HDPI is MDPI x 1.5.

XHDPI is MDPI x 2.

XXHDPI is MDPI x 3.

XXXHDPI is MDPI x 4.

notification icon尺寸：

MDPI - 24 x 24  (drawable-mdpi)
HDPI - 36 x 36  (drawable-hdpi)
XHDPI - 48 x 48  (drawable-xhdpi)
XXHDPI - 72 x 72  (drawable-xxhdpi)
XXXHDPI - 96 x 96  (drawable-xxxhdpi)