[SetupWizardLib] Add support for require scrolling

Add SetupWizardLayout.requireScrollToBottom method that will register
a RequireScrollHelper on the layout. When the helper is registered
and the content view can scroll, the next button will be hidden and a
down-arrow button is shown, which will scroll the page down when
clicked.

Change-Id: Ib9ddcbeec24169cc00265fe107deb1b5099cba8d