surpport object-based edit mode, big refactoring is needed.

[naiteluo]

Expected new features and design:

• Object create by user interactions should be EDITABLE.
  • maintain low cost virtual object tree/pool to surpport post-operation on object.
    • can be easly identified
    • better life-circle
    • stateful
    • have hit box
  • Draw object can't be simple render to rendertexture after user finishing operations. New way of optimizations are needed.
  • For now, GraphicHandler is strictly limited and inconvienct to use. Try to extend PIXI Container to create a internal special container to replace GrahpicHanlder.
• Select mode surpport.
  • selected object's ui is provided as a NEW PLUGIN: EditPlugin.
    • it handle all user interactions after plugin being activated.
    • it might be able to filter/search object by doing hit test.
    • it provide visual handles and boxs around selected object, intercepts user interaction and react to edit operations.