Issue description

As the title states, virtmanager needs dconf. Otherwise, a lot of quirks appear, as virtmanager heavily relies on dconf to store settings (like default connection to libvirt, vmviewer specific things like autoresize and so on).

Steps to reproduce

• run an window manager / desktop environment which does not provide dconf
• start virtmanager
• add a default connection
• restart virtmanager, see how the connection disappeared

Technical details

• system: "x86_64-linux"
• host os: Linux 4.14.90, NixOS, 18.09.1799.b9fa31cea0e (Jellyfish)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.1.3
• channels(root): "nixos-18.09.1799.b9fa31cea0e"
• channels(wucke13): "nixpkgs-unstable-19.03pre161900.61c3169a0e1, nixos-unstable-small-19.03pre161392.50bb0afa7ce, nixos-unstable-18.09pre150708.083220867c7"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos