Two frame animated models

[Robadob]

e.g. FGPU1 Pedestrian rendering.

[Robadob]

Currently model is set via

    /**
     * Use a model from file
     * @param modelPath The path to the model's file (must be .obj)
     * @param texturePath Optional path to the texture used by the model
     */
    void setModel(const std::string &modelPath, const std::string &texturePath = "");
    /**
     * Use a stock model
     * @param model Model from the libraries internal resources
     */
    void setModel(const Stock::Models::Model &model);

To support KeyFrame'd animation models we'd need an alt version, e.g.

    /**
     * Use a keyframe animated model from file
     * @param modelPathA The path to the model's first file (must be .obj)
     * @param modelPathB The path to the model's second file (must be .obj, have the same number of vertices/polygons as the first file)
     * @param lerpVariableName Name of the agent variable used for controlling linear interpolation between the two frames. This must be a `float` type variable with a value in the inclusive-inclusive range [0, 1]
     * @param texturePath Optional path to the texture used by the two models
     * @see setModel(const std::string &, const std::string &) This version can be used to provide agents a static model
     */
    void setKeyFrameModel(const std::string &modelPathA, const std::string &modelPathB, const std::string &lerpVariableName, const std::string &texturePath = "");
    /**
     * Use a stock keyframe animated model
     * @param model Model from the libraries internal resources
     * @param lerpVariableName Name of the agent variable used for controlling linear interpolation between the two frames. This must be a `float` type variable with a value in the inclusive-inclusive range [0, 1]
     * @see setModel(const Stock::Models::Model &) This version can be used to provide agents a static model
     */
    void setKeyFrameModel(const Stock::Models::KeyFrameModel &model, const std::string &lerpVariableName);

Internally, we can have an additional var for 2nd model/lerp var name, and assume its static if neither is set.

Bit more complicated, because different agent states can have different models. Possible there will be an issue/bug, if a user tries to mix static and keyframe'd, would need to check on this when working on it.

cc @mondus

[mondus]

Yeah I like this its nice and tidy.