ludus. Move position from a object to entity.

Move the position field from object to entity.
Change position access methods in objet to virtual.
Add implementation of position access methods to entity.
This is a preparation step for camera implementation.
Revert "ludus. Move position from a object to entity."

This reverts commit 779d41e59d0d2b2fb8fc0b6ee5de197bcbc47e6e.
The camera will be part of a render pass so this change is not needed.
pingo. Add camera.
pingo. Add GLES camera.