Linux/Octave: Adapt Screen+Waffle build for current 3.0.12

- Now also use GStreamer-1.x for Waffle builds.
- Test-Rebuild Screen for 64-Bit Octave on Linux for Waffle/Desktop.

-> Testing under X11/GLX, X11/EGL, Wayland/EGL and GBM/EGL so
   far sort of works ok'ish. At least under Weston i can get
   some basic stims working, although all input handling is
   currently missing from PTB on non-X11. GBM doesn't crash,
   but doesn't display anything. Baby steps...
Linux: Improve basic Wayland compatibility.

- KbCheck and GetMouse now detect on Linux if they are running
  without a X-Server, and no-op if so. Non X11 input device
  support isn't implemented yet, so a no-op is much better than
  crashing the runtime.

- Screen() with Waffle now detects if it is running under a Wayland
  compositor and selects the Wayland/EGL display backend by default
  if user doesn't explicitely requests a different backend.

-> Screen for 64-Bit Octave on Linux rebuilt with Waffle backend
   for testing.

-> Works under regular X11 with GLX or EGL as always.

-> Works under Weston on top of X11 with X11 based input handling
   and Weston/Wayland based graphics - with bad timing of course.

-> Works under Weston directly on DRM/KMS VT framebuffer with
   good visual timing, but without any keyboard/mouse input.

Babysteps...