qt-kiosk-browser: add a systemd unit and adjust default URL

This is the first part of the fix for issue https://secogroup.atlassian.net/browse/YT-74

Following changes are introduced in this MR:

• add a qt-kiosk-browser.service service file to Yocto rootfs by adjusting a qt-kiosk-browser recipe;
• change a default URL to edge.seco.com for qt-kiosk in corresponding configuration file (/etc/qt-kiosk-browser.conf).

Note: the integrated service is disabled out of box, so after boot it should be enabled/started manually:

systemctl start qt-kiosk-browser

The second part, which changes default URL in hints.md is handled in following MR: seco-ne/yocto/manifest!1752 (merged)