Add wayland support to appimages

[zjeffer]

qt.qpa.plugin: Could not find the Qt platform plugin "wayland" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: xcb.

Current workaround: running the appimage with --platform xcb, which runs it in XWayland. It's kind of glitchy but usable.

[guihkx]

I'll link here my last experience at attempting to add Wayland support to AppImages. It might be helpful in case someone wants to pick up where I left:

• Try let the window manager move the window, fixes #429 #445 (comment)