Draft: example of a working Flatpak manifest file

[DodoLeDev]

Hi everyone! 👋

In order to give more visibility to this awesome application, I am suggesting this initial draft for a flatpaked version of Friction.

As you may see in the file in the MR, several changes to the packaged files are required. I have managed to apply them in the package procedure, so that maintainers don't have to bother with it.

As-is, the package is really "dirty": I didn't manage to compile the source code by myself, so I use a pre-compiled binary directly fetched from Github releases.

However, I tried to lighten the package size, by removing dependencies already provided by the runtime (it's the reason why there is so much files deleted during the package procedure). Its installed size is now 70MiB (~15MiB less than the uncompressed tarball)

Try it by yourself with the following commands:

mkdir build
flatpak-builder --force-clean --install build graphics.friction.Friction.json

Notable points:

• I wanted to follow the principle of least privilege, so the app have the minimal dependencies required to run.
• Because this app is written in Qt, I used the KDE Runtime, which provides a bunch of Qt-related libs. You can probably save a lot of space if the manifest file could compile the program with the runtime libs.
• The app doesn't use any XDG Portals, so the save/open dialog requires the entire home folder permission. Maybe a feature request?