0031757: Visualization - Prebuild BVH for Select3D_SensitiveEntity in separate threads

0031757: Visualization - Prebuild BVH for Select3D_SensitiveEntity in separate threads

- Added a new mode in SelectMgr_ViewerSelector for computing BVH for Select3D_SensitiveEntity in background which can be activated via method SelectMgr_ViewerSelector::SetToPrebuildBVH(). Default behavior has not been changed.
- New class SelectMgr_BVHThreadPool manages background processing of BVH building queue.
- Added Select3D_SensitiveEntity::ToBuildBVH() method that checks if BVH (if it used) is in invalidated state. Defined this method for all standard classes inherited from Select3D_SensitiveEntity.