[GNOME LaTeX] Gnome-Latex in flathub

[othko97 gmail com]

Hi!

Recently an extension for TexLive was released on flathub, and as this
was the main blocker for the issue [0] to distribute a flatpak on the
bug tracker, it is feasible to create a flatpak now.

I have created a working manifest and opened a PR [1] to the git repo,
but as the project is no longer maintained I don't expect it will be
merged. However I would like to publish the manifest to flathub, if
there are no objections.

As a last caveat, in order for flatpak to find the logos they had to be
renamed, and as my PR won't be merged I need to point the manifest at
my fork, where I renamed the logos to `org.gnome.gnome-latex.*`.

Is this okay with everyone?

Thanks,

Tom

[0]: https://gitlab.gnome.org/GNOME/gnome-latex/issues/39
[1]: https://gitlab.gnome.org/GNOME/gnome-latex/merge_requests/17