[aform] Link field with tuple-like data

[agritheory]

• Title
• Right facing arrow in Bootstrap-style input group to navigate to the document, no-op if no FK/id exists
• Allow for extra field fields for formatter purposes

[Alchez]

@agritheory since this affects a bunch of places in the code and I wanted to not have AForm cross the form-component library boundary, I've added an initial spec as a private gist. Can you read through it and let me know if it's making the correct opinions?