add Gleed2D editor support

GLEED2D (Generic LEvel EDitor 2D) is a general purpose, non tile-based Level Editor for 2D games of any genre that allows arbitrary placement of textures and other items in 2D space. Levels are saved in XML format. But it only support XNA with C# API officially. I just add new source file written to support loading Gleed2D level file into Cocos2d-x scene.