Refactor app view structure

Most of the logic that was in StandaloneApp.render has been moved
down to RenderViewPage. This will allow StandaloneApp to route and
switch between multiple full-page views (e.g. search page).

@jbeezley @patrickoleary You guys should merge this into your topics since it is a major refactor of the high-level app view structure and will probably affect your work.