Improve Flatpak permission icons
Previously we were using a mixture of symbolic and colorful icons, due to our inability in Plasma 5 times to specify one or the other. That's not the case in Plasma 6 anymore, so let's use all symbolic ones. Also switch out some awkward icons for better ones.
I know the text of a lot of these permission strings isn't ideal, but that'll be handled in another MR.
| Before | After |
|---|---|
 |
 |