[Feature/Enhancement] Support for Debian 13 (Trixie)

[borisovg]

The debian package is not installable on Debian 13 due to missing dependency libqt5webkit5.

Also, PPA installation instructions need updating due to "apt-key" no longer being available. Something like this should be used for installing the public key instead:

wget -qO - http://www.mindforger.com/gpgpubkey.txt | sudo tee -a /etc/apt/trusted.gpg.d/mindforger.asc

[johnblommers]

I've attempted and failed to build a working AppImage of MindForger that runs on Ubuntu 15.10.
Here's hoping MindForger gets a fresh build to address Debian 13, upon which Ubuntu 15.10 is built.
Damn but nothing else I've tried beats MindForger.