Iterations report page assignee images too small

Proposal

On the iterations page within the Issues table at the bottom, the assignees images are quite small. This makes it difficult to determine who I'm looking at. They are set to 16px x 16px which appears to be the size within the Pajamas assets, but while I believe this may be a standard size for icons, I don't think it should apply to avatars. My proposal is that we up the size to 24px x 24px.

Before	After

cc @gweaver This is a small usability issue I'd love to see get worked on soon.