BUILD: Multi-Stage the docker build process

Generate build dockers used to build the application in appimage mode or
in a zip file for windows.

Still some issues with wayland on linux for the appimage, so we force
xcb rendered when not relying on gtk (gnome, xfce, etc, but not tested
there...)

Logs are:
	[07:59:29 DEBUG CC::WINDOW] module_qt_window.cc+62:mod_new: initializing a new window
	[07:59:29 DEBUG CC::WINDOW] module_qt_window.cc+70:mod_new: waiting for the new window, active wait...
	qt.qpa.wayland: Failed to load client buffer integration: "wayland-egl"
	qt.qpa.wayland: Available client buffer integrations: QList("wayland-egl")
	QOpenGLWidget is not supported on this platform.
	QRhiGles2: Failed to create temporary context
	QRhiGles2: Failed to create context
	Failed to create QRhi for QBackingStoreRhiSupport
	QOpenGLWidget: Failed to create context
	[07:59:29 ERROR CC::WINDOW] mpvwidget.cc+268:handleMpvEvent: Should not get event idle (id is 11)
	[07:59:29 DEBUG CC::WINDOW] mpvwidget.cc+216:handleMpvEvent: Detected pause
	[07:59:29 DEBUG CC::WINDOW] mpvwidget.cc+247:handleMpvEvent: Applying unpause
	[07:59:29 DEBUG CC::WINDOW] mpvwidget.cc+224:handleMpvEvent: Detected unpause
	[07:59:29 DEBUG CC::WINDOW] mpvwidget.cc+232:handleMpvEvent: Detected idle
	[07:59:29 DEBUG CC::WINDOW] mpvwidget.cc+234:handleMpvEvent: Applying idle
	[07:59:29 DEBUG CC::WINDOW] module_qt_window.cc+75:mod_new: new window OK!
	QOpenGLWidget: Failed to create context
	Segmentation fault (core dumped)