Lay UI foundation for how we want to add/edit Datasets

[chadoh]

When you click "create dataset", here's what should happen:

• A new, blank dataset is created in the database immediately (this differs from normal Rails stuff)
• You get redirected to the "show" page for this new dataset
• The "Title" field, nice and big in an >h1< at the top, is a form field, with "Untitled" as placeholder text, and is autofocused
• The "Title" field has its own "Save" button
• There's also an empty "description" field, with its own save button
• Right now, these are the only two editable fields on Dataset, so they will be the only things shown
• If a user who isn't logged in visits the page for this dataset, they should not see the forms, but only the values of those fields

Eventually, we'll want to pretty this up with some fancy JavaScript stuff, but this works for now.