BGE - new read-only attribute in KX_GameObject python api (LOD level)

Added a new "current_lod_level" property to the python api of
KX_GameObject. The property returns the current lod level of the game
object. The purpose of the property is activate logic routines only when
an object is at a certain lod-distance from the camera, avoiding to
separately recomputing the same distance in the logic script. Usage in
python script might look like:

owner = bge.logic.getCurrentController().owner
lod_level = owner.currentLodLevel
if lod_level == 0: ...do something
else: ... object might be too distant

Reviewers: dfelinto, kupoman, moguri

Reviewed By: kupoman, moguri

Subscribers: lordloki

Projects: #game_engine

Differential Revision: https://developer.blender.org/D978

doc/python_api/rst/bge_types/bge.types.KX_GameObject.rst

@@ -432,6 +432,12 @@ base class --- :class:`SCA_IObject`
       If true, the object's and children's debug properties will be displayed on screen.
 
       :type: boolean
+      
+   .. attribute:: currentLodLevel
+
+      The index of the level of detail (LOD) currently used by this object (read-only).
+
+      :type: int
 
    .. method:: endObject()