Create agreement step (2d)

[htpvu]

• Add display area for agreement text, with interaction to “agree” checkbox (?)

[jabrah]

• Be able to cycle through multiple agreements, each with separate elements to indicate agreement

[jabrah]

For now, we can keep agreement text in static files. We currently don't have details on agreements, so we can have a few placeholders.

How should agreement state be saved, so this step can be initialized? Is it enough to simply have a list of agreement keys that the user has agreed to?

submission: {
  ...
  state: {
    agreements: ['one', 'foo', 'bar']
  }
}

We should have a client side model object for state, but it should be stringified when persisted to Fedora.