Put background image on all pages

[gsehrlich]

Is your feature request related to a problem? Please describe.
Plain white background is too stark.

Describe the solution you'd like
@hawser chose an image of the Port of Oakland. Make this the background image as specified in the Figma file (linked below).

Responsiveness: the image should be the same height as the content.

Additional context
Here's the Figma file: https://www.figma.com/file/YJGrbzkh0dei32uAH3Q5m3/WOAQ?node-id=0%3A1

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For Developers

Affected Components
Not sure, but ideally it would only need to be changed in one place to affect all pages.

Technical Resources

Design Documentation
see above

Testing Outline