Add Model-level DeOldify Ability

[CyFeng16]

Changes were done as follows:

1. Add model-level DeOldify ability and combine it with our I/O.
2. create a single docs folder for multi-languages guidebooks.
3. Improve readability of current README.md.
4. Add Chinese guidebook.
5. Fix incorrect arguments setting of --high_resolution(-hr) in DAIN, which enable frames splitting for high-resolution video (1080p+).
6. Set default hardware to GPU0 to avoid manual hardware selection in DeOldify.