feat: flatpak preparations (v2) + metadata update

[ludg1e]

Reference issue: #147

This PR adds the required files so flatpaks can be build under the Flathub organization infrastructure on GitHub, as well as it improves slightly the AppStream XML metadata.

Todo list moved to the reference issue

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Changes regarding v1 PR (#416) :

• Added argument --add-opens java.base/java.net=ALL-UNNAMED to the bash executable
• Changed the manifest logic so it pulls files from the source repo (this one)
• Tried to use as much as possible the original metadata files

Current status:

• The entire process should be automatic and will be done (when published) by the Flathub buildbot (it updates the manifest in the Flathub repo per each new release of ipscan in this repo -> the bot checks for new releases and grabs the linux64 .jar file)
• Only per each new release a new entry should need to be added under /ext/deb-bundle/usr/share/metainfo/ipscan.appdata.xml and /ext/flatpak/org.angryip.ipscan.metainfo.xml with the release number, date, and the url to the release tag of GitHub
• Uses OpenJDK 11 Freedesktop runtime from Flathub

[ludg1e]

@angryziber if there's something missing or you want to change something let me know please

Thank you and have a nice day

[ludg1e]

Hello, any update?

[Laserlicht]

Any update on this?
@angryziber

[ludg1e]

Hello.

I'm no longer interested in working on this PR.
There are other alternatives out there that don't require OpenJDK, plus they're much more feature rich as well as simple to use (e.g Zenmap, nscan or What IP on Flathub).

Have a nice day!