I see it as the first step in simplifying the route navigate of the
JavaScript app by removing BlankWelcomePage from _getRouteToRender. From
a faraway point of view, the app is at the route at which it is not in a
conference. Historically, the route was known as the Welcome page. But
mobile complicated the route by saying that actually it may not want to
see the room name input and join button.

Additionally, I renamed BlankWelcomePage to BlankPage because I don't
think of it as a WelcomePage alternative but rather as a more generic
BlankPage which may be utilized elsewhere in the future.

I plan for the next steps to:
* Merge Entryway, _interceptComponent, and _getRouteToRender in one
React Component rendered by AbstractApp so that the whole logic is in
one file;
* Get rid of RouteRegistry and routes.