kcms/tabbox: hardcode app names and icons in the preview

Right now the thumbnails are hardcoded, but the app names and icons are not, and change based on the user's default apps. This is nonsensical; the thumbnail won't match what the name and icon claim the app to be.

Let's stop doing that and instead just hardcode the names and icons to match the thumbnails.

BUG: 499106 FIXED-IN: 6.4.0

I chose 6.4 due to new strings, though I guess it's not the end of the world if backported since the strings are branded app names and those are often not translated.