Remove broken caching

Since we're no longer iterating over the entire list to get to the
article, we don't need to cache the value. We're now retrieving an
article from a hash using its id as the key, which is O(1).
Remove unnecessary config

The default controller is an ApplicationController and the store doesn't
even work yet.
Render the outlet even without articles

There was a weird catch-22 where the outlet wasn't being rendered
before, which kept the new-article form from being rendered. So you had
to have at least one article in order to create another one. I found
that kinda funny.
Add initial serializer implementation