Add routing for items.

- make the controller name required for the fourth case (i.e. no default).
- add fifth case to routes in bootstrap for items.
- make an empty url point to the root item, but an invalid url throws an error.
- revert back to using action_show() in Photos, Albums, and Movies controllers.
- revise action_show() to get item model from request.
- remove Albums controller action_index().