Created by: qingqing01
- rename: PaddleVideo -> video, PaddleGAN -> gan, Paddle3D -> 3d_vision
- remove models/PaddleSlim
- add PaddleDetection as submodules.
- Update link in models/README.md and models/PaddleCV/README.md
see https://github.com/qingqing01/models/tree/release/1.7-2/PaddleCV