Use larger app icon for a workspace with one item

[danirabbit]

Problem

When a workspace only has one item, the icon inside of it is very small

Proposal

For workspaces with a single item we should use a larger icon

Prior Art (Optional)

We used to use a large icon in the old workspace switcher

#387

[danirabbit]

Closing my previous draft branch because the way icon size is set has changed a bunch since then. But I did get 6 thumbs up and no thumbs down on that branch so it seemed like a popular idea