Refactor glTFLoaderInterface

[Ybalrid]

Currently the interface looks like this :

    ///Plugin accessible interface that plugin users can use
    struct glTFLoaderInterface
    {
        ///Polymorphic dtor
        virtual ~glTFLoaderInterface() = default;

        ///Get you an item from a GLB file loaded inside an Ogre resource group
        virtual Ogre::Item* getItemFromResource(const std::string& name, Ogre::SceneManager* smgr) = 0;

        ///Get you an item and transform from a GLB file loaded inside an Ogre resource group
        virtual ItemAndTransform getItemAndTransformFromResource(const std::string& name, Ogre::SceneManager* smgr) = 0;

        ///Get you an item and transform from a GLB or a GLTF file from the filesystem.
        virtual ItemAndTransform getItemAndTransformFromFileSystem(const std::string& name, Ogre::SceneManager* smgr) =0;

        ///Get you an item from a GLB or a GLTF file from the filesystem.
        virtual Ogre::Item* getItemFromFileSystem(const std::string& fileName, Ogre::SceneManager* smgr) = 0;

        ///Get you a mesh and a material datablock from a GLB in the resource manager
        virtual MeshAndDataBlock getMeshFromResource(const std::string& name) = 0;

        ///Gets you a mesh and a material datablock from GLB or a GLTF file from the filesystem
        virtual MeshAndDataBlock getMeshFromFileSystem(const std::string& name) = 0;
    };

The XXXFileSystem and XXXResource methods are mostly identical. A simple flag could singal where we are supposed to load from.

Returning an Item, or a Mesh, or an Item with a transofrom (or a mesh with a transform,t hat is not possible right now) should be handled better.