This adds a new UI pkg for configuring/running os-installer, which is a nice little OS installer thing that we can use to install pmOS on laptops/tablets and stuff like that.
It runs under GNOME desktop, to support accessibility features and operate as a "live CD" like many other distro installer things do.
Under the hood, this is using pmbootstrap to install pmOS onto some local storage selected by the user in the os-installer UI. It defaults to targetting the device that the user is booted into. It will support FDE once a new pmbootstrap release is made with pmbootstrap!2538 (merged) in it.
Currently it only offers GNOME, KDE, and xfce desktop environments, but it's pretty easy to add more later.
