Replaces hero image with smaller image, updates CSS for hero image

[ghost]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Description

This PR replaces the image with a smaller image, one that promotes vision zero better than the earlier image.

I am currently working on making the hero image responsive for Mobile viewports.

The image is no longer

• So large (new file size is 1.1mb)
• Misrepresentative of our app's mission

Checklist

• [] I have updated the documentation accordingly
• [] I have written unit tests

Fixes scrapd/scrapdviz#184

[ghost]

Hey Remy, again I'm still working on making the hero image responsive for Mobile viewports. Here's a preview of the homepage. What do you think?

[rgreinho]

Love it! It really looks great!