Porting Flask to Django Framework

- [x] RESTful Resource API (Song, Skill, WarmUp, SongSkill, WarmUpSong)
- [x] **new** Admin Interface
- [x] **new** Browsable API
- [ ] Test Case
- [ ] Deployment

Don't merge this branch yet, until everyone agree to do so. Because it completely replace the whole logic that we have ever done in Flask Framework.