105 restore request this collection button for collections with no contents

[Nealium104]

This PR restores the ability to request UK collections that have no contents listed. These previously had a "Request This Collection" button, but that behavior was removed during limestone-rewrite work.

Changes

• Adds an "Add Collection to Request" button to the Requests box for UK collections with no contents
• Keeps the button outside the request dropdown so it is always visible
• Uses the existing request form for retrievals, reproductions, and saving for later
• Adds the checkered divider between the controls when the panel is open

Fixes #105

Screenshots of implementation

[cokernel]

Verified functionality.

Verified that the expected request_options shows up on requests-libraries when requesting a collection.

This looks good to me.