Move the additional settings to the top of AppInfoDashboard

Based on the Android S design, move additional settings preference
above the Notifications preference and use SpacePreference to draw
the horizontal divider below AppButtonsPreference since the additional
settings preference is only visible by condition.

Also remove initialExpandedChildrenCount to expose all preferences.

Bug: 174964524
Test: robotest & visual with turning on/off silky home
Change-Id: Ife1d37820e44f8e12af4ed37ed66a29281366b50