Feature: Added index action for link controller

I need to think about how I want to do this, because if this link controller
is going to continue to exist, it will be nested within the box index, which
will be the real "index" page.

I almost think it would be easier to just have a the box model that has 7 fields,
name, 3 titles, and 3 links. That way I could use the put/patch HTTP request and
wouldn't have to add a new link and hide the old one. It makes sense because it's
editing rather than producing, but it is hard coding only 3 links, so it would
be difficult if you ever decide you want more than that.

But what is brevity box without the limit of 3 links?
Feature: Add a show action for the link controller

This almost certainly will end up being deleted, because it doesn't make sense
to have a page just to show one link. See my commit message on adding the link
index. More and more I'm thinkin it should just be the box controller that has
3 links in it and a name. Or maybe the name would be tied to the user model.
Is the user model even going to be complex enough to be separate?
Feature: Set the links index as the homepage

Also link to it from the add new link page etc. Again, I think I will replace
this with the box index, or nest this inside the box index. I need to follow
the tutorial a little further to see which makes the most sense.