Experimental, compiles but does not work.
Fix duplicate calls to OEngine.  Use correct position, rotation and scale.  Debug draw not working.
Debug rendering toggled by double clicking the right mouse button.  Raycasting works, but inaccurate.
Added debug lines to show ray hit position.  Added highlighting the Entity hit by the ray.  Incorporated user setting far clip distance.
Fixed issue with mouse picking accuracy.
Minor refactoring and cleanup.
Make gcc happy.
Avoid Ogre exceptions and null pointers.
No physics or mouse picking for object preview.
Convert PhysicsSystem to a singleton.
Store object reference id to RigidBody instead of scene node handles.
Use QString rather than std::to_string
Merge remote-tracking branch 'upstream/master' into mouse-picking
Add settings to enable/disable debug rendering of mouse picking.
Add terrain collision.  Support visibility mask for objects and terrain.
Cleanup bullet objects in the destructors.
Use the correct name for deleting objects.
Report terrain position on cursor position.
Cleanup for better legibility.
Move debug rendering code out of PhysicsSystem.