fixed adding renderables with already loaded models; fixed undo/redo
fixed adding renderables with already loaded models; fixed undo/redo

dreamsxin/LuxEngine,dreamsxin/LuxEngine,galek/LumixEngine,gamedevforks/LumixEngine,gamedevforks/LumixEngine,zhouxh1023/LumixEngine,zhouxh1023/LumixEngine,JakubLukas/LumixEngine,JakubLukas/LumixEngine,JakubLukas/LumixEngine,galek/LumixEngine