Implement the Scroller component to provide scrollability for components.

In the current Uploader, there's great useful functionality for handling scrollable views. This needs to be split out into a self-contained component with a convenient API, including:

scrollToTop()
scrollToBottom()
scrollToElement(element)

This is the sort of component that should probably do its own self-rendering when the requisite DOM wrappers aren't already present.

dev-iteration43