it running, but maybe have many bug.

plasma-workspace plasma-desktop kscreenlocker etc. their qml is cyclic
dependence, no idea how to cut cyclic, so i change qtwrap to set
QML2_IMPORT_PATH from `=' to `prefix', make them get system's env.

change sddm services to add some environment-variables make breeze theme
work.

and have many bug, such as screenlocker is cann't unlock, wayland is not
work, and something other.

you can try it.

username is plasma
password is plasma

``` bash
`./pre-inst-env guix system vm gnu/system/examples/plasma.tmpl` -net user,hostfwd=tcp::2222-:2222 -net nic
```