Automatically rotate image based on accelerometer values

Device orientation is provided by net.hadess.SensorProxy
iio-proxy-service. If there is no accelerometer on target platform,
then window orientation from X11/wayland is used as before.

flatpak/me.gapixels.Megapixels.yml

@@ -27,6 +27,9 @@ finish-args:
   # camera shutter feedback
   - --talk-name=org.sigxcpu.Feedback
 
+  # accelerometer sensor for orientation
+  - --system-talk-name=net.hadess.SensorProxy
+
 modules:
   - name: megapixels
     buildsystem: meson