Include a nicer terminal

The devkit image currently ships with GNOME Terminal 3.30, which still uses the old app icon style, and doesn't have a headerbar (both were introduced in 3.32). It would be nice to either get a more recent gnome-terminal version, or kgx (probably with a more generic app icon) as the default terminal on the image.

Kgx is a modern, minimal terminal for GNOME. Its design and feature set make it a perfect fit for the phone (even the new headerbar version of g-t would require a lot of UI work to be fully adaptive).