Add-ons for Veyon 4.4

[tobydox]

Just in time for the release of Veyon 4.4 the add-ons have also been updated. From now on all add-ons can be tested without a demo license key for a limited time. So if you always wanted to test e.g. the Internet Access Control add-on, you can do so easily after updating to 4.4.

Further information on the add-ons can be found at https://veyon.io/addons/