Make AdaptiveIcon support different inset

Settings used AdpativeIcon for injection icons of homepage and the
rainbow icons of connected devices. In the past, the default inset was
6dp which is to generate the 36dp icon. Based on the Android S design,
we would like to apply different size to the homepage icon. Therefore,
make the AdaptiveIcon to support different insets.

Fixes: 177213699
Test: robotest & visual with turning on/off silky home
Change-Id: I1739eeb58e362f24719ef2476c442c867d0ecb3a