Rename Renderer's renderables to another name
- rename m_pRenderables to m_pRenderablesVector
- add this variable to constructor's init list
Remove Todo comments
- some comments for TODO has been done, and the notes has been added to notebook
Add Scene class and OGL Clear Scene
- add Scene class, in which it manage the Renderable's Vector, it owns the lifecycle of Renderables
- Scene will maintain and hold a vector of Renderables,  new and delete the vector of Renderables
- Scene will feed the Geometry, Mesh, Shader, IA in Renderable in its Init(), and destroy them in its Destroy()
Add Scene to Application
- AndroidApplication will keep one scene for current scene
- the scene is assign to GLBasicScene() for glClear calls now, and MakeCurrent()
- Split AddTasks()  to InitTask() and AddTask()
- InitTask() will new scene and make it current for Renderer
- Remove EGLRenderer's default glClear calls, and these glClear calls are placed in the first place of Scene's Renderable vector
    - EGLRenderer did not have any glFoo calls, but only eglFoo calls now
Comments for Todos
- just some comments for todos