Filament 1.15.1 + ARCore 1.29.0 + New VideoNode features + Fixes + Documentation

• Filament 1.12.8 -> 1.15.1
• ARCore 1.26.0 -> 1.29.0
• VideoNode:
  • Fixed wrong positioning (#217)
  • The VideoNode is now centered and above a ParentNode.
  • Added a new flag to enable a look to camera feature.
  • With the function call setRotateAlwaysToCamera(boolean rotateAlwaysToCamera), the VideoNode will always look to the Camera
    (the user). The best effect can be achieved with a Video shown on a Plane.
• Add Proguard ARCore keep rule
• Fixes:
  • Call setDisplayGeometry after Session is resumed (#267): Fix wrong behaviors when resume is called too late
  • Fix ShapeFactory cube : Reversed front/back vertices (#272)
  • Initialize ViewRenderable with transparent texture and set it in material right away (#273): Fix default texture first frame showing the camera stream
• Documentation