Removed Devise, added basic authentication

Here is what I did:

I created a migration to get rid of the fields that Devise left behind. I also got rid of the Devise files.
The basic authentication is there. Data sets, sources, and tags can not be modified or destroyed by non-users. It will just redirect you to the login page.

One caveat: If you login with the wrong password, it will give you a 'template missing' error instead of returning you to the login page. I cannot figure out how to display the error in the view using form_tag .

I know we talked about users only being able to delete their data sets, sources, and tags and not others', but I would rather set up Rspec and get some tests up before I tackle those issues.
Ooooohhhh! I noticed that you changed this from Rails's default, which had been `@dataset.update(dataset_params)`, and you made it use `update_attributes` instead. I wasn't sure what this whole `update` thing was; I always tend to use `update_attributes`. So I went and looked it up. Exciting news! `update_attributes` is [just an alias for `update`](http://apidock.com/rails/ActiveRecord/Persistence/update_attributes)! So it's completely personal/team preference for whether to use `update` or `update_attributes`. Which do you like more?

Also, since I'm commenting on this line anyhow, it's worth pointing out that the indentation is one space off here, too. :information_desk_person: