Draft: Allow setting and replacing the app icon on the app edit screen
This fixes #256
The App icon can be added or replaced on the App Edit screen
I didn't add functionality to remove the app icon like other fields (screenshots, feature graphic), which was partly laziness, but also it doesn't seem that useful. I can add it if desired though.
Also, the new field doesn't look great (the drop target is wide like the feature graphic), yet
Edited by Steven McDonald