[Rails][Imports] Move import form from the bottom of the list views to a new view

[lauramosher]

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Context:

Importing Stories, Places, and Speakers is currently done by an inline form at the bottom of the respective index/list pages. This works well enough when there are no or very few items in the list, but can quickly get buried when there are many.

Let's make it so the import form is it's own view. This can be done by either making a new page view, or introducing a modal view of some kind.

Acceptance criteria:

• [ ] Index/list pages should have a new button called "Import" that redirects to the new import form (modal or page).
• [ ] A new Import view that accepts the same file type and submits to the same route
• [ ] Once created, it redirects back to the index page.

Assets

This could be worked in conjunction with #589.

The form at the bottom of this image is what should be moved into its own view.

[Aliciawyse]

👋🏾 hello there! I'd like to take this one :-)

[Aliciawyse]

~This new view should live here correct? https://github.com/Terrastories/terrastories/tree/master/rails/app/views/admin~ nvm :-)