Simplify display of images in Plugin Repository

[Gabe-Mitnick]

I'm a big fan of SwiftBar, thanks for maintaining it!

This PR fixes a couple of small visual issues I noticed in the Plugin Repository window

• When an image for plugin is available, it's too small
• Extra corner radius on the modal view, even though the system UI already includes a corner radius

Before	After

• When the app icon is displayed as a fallback image, the opacity and size are different depending on whether the image URL is missing (small transparent icon) or the image URL fails to load* (big opaque icon)

*Lots of plugins from the xbar repository JSON have image URLs that point to 0-bit files, like https://xbarapp.com/docs/plugins/AWS/cloudwatch-alarms.30s.py.png, even though the plugin's contents contain a valid image URL. This PR doesn't fix that issue 😅

Before	After

^ No change to settings page — this plugin with no image URL still doesn't show the app icon.

• ImageVIew.swift had a typo in the filename

[melonamin]

Thanks! I'll merge it a bit later.