allow launching desktop file with uwsm

[abihf]

use uwsm to create systemd scope for each app.

[nwg-piotr]

I have never heard about it. Why should we rely on a work-in-progress thing, not yet even packaged in main Arch repos? How is the drawer going to behave on non-systemd distros, e.g. Slackware? @mac-a-r0ni, what do you think?