virt-manager: update to 1.0.1, update dependencies, add gtk3 support

This work is based on @bjornfor branch:
https://github.com/bjornfor/nixpkgs/tree/virt-manager-version-bump

- Vte, add gtk3 support, enable introspection, update to 0.35.90
- Spice-gtk, add gtk3 support
- gtk-vnc, add gtk3 support
- Add libvirt-glib (thanks @bjornfor)

TODO (not major): fix virt-manager complaining about avahi