Ubuntu to switch back to GNOME and will use Wayland

[In a blog post from Mark Shuttleworth](https://insights.ubuntu.com/2017/04/05 /growing-ubuntu-for-cloud-and-iot-rather-than-phone-and-convergence/), Canonical will stop work on Unity 8 and the desktop server Mir. In Ubuntu 18.04, GNOME and Wayland will be the desktop display technologies. This effectively cancels their work on phones, tablets, and convergence.