Flatpak manifest added

[christf]

this provides a flatpak manifest. The flatpak can be built and run with

flatpak-builder --force-clean --user --install-deps-from=flathub --repo=repo --install builddir org.flatpak.navit.yml 
flatpak run org.flatpak.navit

• embed into one of the pipelines, so this falls out of a PR run and on every release
• test audio output
• test location via geoclue

this closes #1468

[jkoan]

Thoughts:

• Which version of navit should be the definitive version to provide as a flatpak. Flatpaks are used on mobile Linux as well, so it needs to work well on mobile. But desktop as well.
• does it already have access to location? I know there's a portal of sorts already, probably geoclue would be most appropriate for this, but I don't know
• what should be the goal of the flatpak? A navit which works out of the box, or just the same as currently but as a flatpak

[christf]

so far, I have only tried this on my desktop and not on my phone - indeed you are right, this absolutely needs to work too. And I reckon I am still lacking a lot of stuff. Let'S make a list of things to test (top post):

The goal I had in mind: Having an easy distribution mechanism to all distributions. This allows anyone to run a current navit on, say, debian stable.

Most projects I am aware of, there are two flatpaks:

• one for every release
• one on every merge

[jkoan]

Most projects I am aware of, there are two flatpaks:

* one for every release

* one on every merge

That would be the same as I am planning for the fdroid repo, ein release and one dev/nightly variant