Auto build client appimage

[Lejo1]

Appimages are easy to use cross compatible files including everything to run the application.
This PR adds an automated build to create a client appimage using appimagebuilder to the gitlab ci

Such appimages are portable and don't require any additional installations.

Thanks to @An0n3m0us and @Calinou for the helping me out!

PR also removes the old ubuntu:14-04 build with the new ubuntu:18-04 build

To do

This PR is ready to review. Might need some library changes for OS support

• Test on different linux distributions (Done: Ubuntu, Debian)
• Resolve the Problem in the Desktop file (The builder complains about PrefersNonDefaultGPU=true)
• Clean library list

How to test

I created a gitlab Ci for my minetest fork.
Download Appimage

[Calinou]

Resolve the Problem in the Desktop file (The builder complains about PrefersNonDefaultGPU=true)

You can remove PrefersNonDefaultGPU=true from the desktop file using sed when building.

[Lejo1]

You can remove PrefersNonDefaultGPU=true from the desktop file using sed when building.

Thanks, Good Idea! Did that.

[An0n3m0us]

Ubuntu 16.04: libunistring.so.2: cannot open shared object file: No such file or directory
After adding that library, the game works as expected.

I would fix it myself if I knew how these automated builds work xD

Works on a clean installation of Arch Linux (Manjaro Linux 20.1.2).

[Lejo1]

Thanks for the feedback!
I excluded some random libraries cause I thought they weren't needed (also libunistring).
Should work now (When build is done and I changed the link)

[sfan5]

Looks good.

[SmallJoker]

Yes sure, why not. LGTM.