Added new "Citation search" option to the All and Articles tabs of the homepage search box

[djanelle-mit]

UXWS requested that we add links to the Primo "Citation Search" option onto the Wordpress homepage search boxes.

This PR adds a "Citation search" link using the new /citation-search/ shortcut URL to our Wordpress homepage search box on the All and Articles tab.

Confirmed locally and on a multidev, which was reviewed and approved by UXWS.

This work was tracked in https://mitlibraries.atlassian.net/browse/PW-129

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[matt-bernhardt]

This is pretty straightforward. I see it working in the multidev. The mobile view seems non-awful.