Add new adaptive icon for Android

The new logo is awesome, but on Android it uses a "legacy" icon. This means that it becomes small with an ugly white border. The new adaptive icons not only look much better but also match the system icon shape:

Since the margins are different between Plasma and Android, I had to extend the shapes to fill the space. Please excuse the programmer art.

There is also a inconsistency between platforms. I think being consistent with the system guidelines is more important in this case.