Insert date data into cards.
Trying to get date sorting to work correctly.
Move cards/index.html.erb to a layouts partial and add to user view.

The cards partial is now in a partial so that it can be used whenever a
group of cards need to be viewed.  Users can now see just the cards that
belong to them with the same filters and sorting options as the
cards/index view.

This commit also changes the topbar; swapping out `My Account` for `My
Cards` and `My Decks` when a user is authenticated.

Finally `@cards = @user.cards` is added to the show method on the Users controller.