Based on the Android S design to update the homepage icons in Settings
codebase.
Bug: 178363516
Test: visual
Change-Id: I4f83912d118f85d7f13feb023d30431852efe065
Also delete duplicated ic_settings_notifications.xml and point existing
usages to ic_notifications.xml
Bug: 77982107
Test: manual
Change-Id: Ia7896598c6334aa97faf392b17e6bc3c17d58599