[landing] re-add fix: scroll to top on footer link click

Summary:
re-implementing https://phabricator.ashoat.com/D2380 after I messed up a rebase

(gifs are large, preview isn't available, need to click each one)
Before:

Test Plan: Click on page. Use should always be scrolled to top of page.

Reviewers: atul, ashoat, palys-swm

Reviewed By: ashoat

Subscribers: palys-swm, Adrian, karol-bisztyga, boristopalov

Differential Revision: https://phabricator.ashoat.com/D2402