Add AppImage package and enable autoupdate for linux (If installed using appimage)

[raffis]

Is your feature request related to a problem? Please describe

I miss the ability of a more modern app shipment on linux => AppImage.

Describe the solution you'd like

Build and release appimage including autoupdate.

Describe alternatives you've considered

Using the existing deb images.

Additional context

electron-builder and updater support AppImage.