BGE: Fix T48071: Global logic manager

Previously the logic manager was used as a global variable for SCA_ILogicBrick::m_sCurrentLogicManager,
this request to always update it before run any python script and allow call function like
ConvertPythonTo[GameObject/Mesh]. The bug showed in T48071 is that as exepted the global
m_sCurrentLogicManager is not updated with the proper scene logic manager.
Instead of trying to fix it by updating the logic manager everywhere and wait next bug report to add
a similar line. The following patch propose a different way:
- Every logic brick now contain its logic manager to SCA_ILogicBrick::m_logicManager, this value is
  set and get by SCA_ILogicBrick::[Set/Get]LogicManager, It's initialized from blender conversion and
  scene merging.
- Function ConvertPythonTo[GameObject/mesh] now take as first argument the logic manager to find name
  coresponding object or mesh. Only ConvertPythonToCamera doesn't do that because it uses the
  KX_Scene::FindCamera function.

Reviewers: moguri

Differential Revision: https://developer.blender.org/D1913

source/gameengine/Ketsji/KX_Camera.cpp

@@ -1035,7 +1035,7 @@ KX_PYMETHODDEF_DOC_O(KX_Camera, getScreenPosition,
 	{
 		PyErr_Clear();
 
-		if (ConvertPythonToGameObject(value, &obj, true, ""))
+		if (ConvertPythonToGameObject(GetScene()->GetLogicManager(), value, &obj, true, ""))
 		{
 			PyErr_Clear();
 			vect = MT_Vector3(obj->NodeGetWorldPosition());