Info unit images should fall back more gracefully

[Scotchester]

If an image is not exactly square, bad things happen.

Current behavior

• a 300x301 image will not render at the desired 150px width

(there may be other current undesirable behaviors related to 25/75 images, but this is the one we just noticed)

Expected behavior

• the image would render at 150px width, with a height of 150 or 151 depending on rounding

Steps to replicate behavior

1. Create an Info Unit Group with 25/75 layout
2. Add an info unit and upload an image to it with a size of 300x301
3. Preview the page and behold the gigantic image

Screenshots

Current

Expected

[Scotchester]

Title updated to reflect the fact that this can happen on 50/50s, too. (I assume also 33/33/33s, though I haven't witnessed that.)