Add adaptive icon

[Commenter25]

Most apps use an icon marked with a safe zone that can be cropped to different shapes for different styles. Torchie does not do this, which makes it inconsistent with the rest of the system. Fixing this is a minor thing, but a major aesthetic improvement. Notice in my picture below that, besides not fitting the desired shape, the icon is actually subtly bigger than the others.

https://developer.android.com/develop/ui/views/launch/icon_design_adaptive