Add scroll down arrow icon to home page hero image

[jrmerz]

Add a down arrow icon to the hero section that links to the collections section. @wrenaria will design.

[wrenaria]

Option: Instead of relying on conjecture, we could set-up in-person user tests with ~5 people who haven't used the DAMS site before to see if they do or do not scroll. That should be enough users to confirm whether or not the front page actually needs a down arrow to indicate more content.

Alternatively, here is the requested design.

• 50px circle positioned about 2/3 down between bottom of search box and bottom of feature image; color: default-secondary-color, #DAAA00
• iron icon: arrow-downward; size 26px; color: light-primary-color, #335379
• Add Digital Collection header, same text styling as on About page but center-aligned