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.
Hmm... It looks like `set_dataset` is a method that itself sets the instance variable `@dataset` to be a `Dataset` object, and then returns that object. If we expand `set_dataset` here, this line would look like this:

``` ruby
@dataset = Dataset.find(@dataset = Dataset.find(params[:id]))
```

When it's written that way, I think it's pretty clear that this code is redundant.

You _could_ just call `dataset` inside your `def show` definition. Or, you could put [line 2](#diff-e5e5071844e053ff47f15cbf9ebb7646L2) back to how it had been, and get rid of the `@dataset =` lines from `show`, `edit`, and `update`.