Migrate to AppImage

[IGassmann]

We should make the move to AppImage because of the following reasons:

• Add support to auto-update for Linux.
• Incorporate necessary dependencies inside the package.
• Supported by practically all Linux distributions.
• Supported by our building tool.

[TheAssassin]

@IGassmann what happened to the issue? I don't see any AppImage downloads.

[IGassmann]

This issue was a duplicate of #332. AppImage builds are coming with the next release.

[TheAssassin]

I see. Thanks.

[IGassmann]

After discussing the fact that you need to change the file permission to launch an AppImage package, it was decided to rollback our changes and not use AppImage. Our app will still be distributed as a .deb package for the time being.

That step is not intuitive and might result in an unpleasant experience for our users.

A possible solution for supporting non-deb distributions in the future will be to use snap builds.

[probonopd]

It's easy to make an AppImage executable:
https://discourse.appimage.org/t/how-to-make-an-appimage-executable/80

Besides, this is not an AppImage issue but I agree that desktop environments should handle ELF executables that are missing the executable bit more gracefully. Only the desktop environments can change that, so please open issues with them if you think this area needs improvement.

Please see AppImage/AppImageKit#374.