Add wrapper for Skycoin REST API v0.27.0

**Feature description**
Add Python wrapper for Skycoin REST API in version 0.27.0

- [x] Generate Python wrapper for skycoin REST API in `lib/skyapi`
- [x] Mention in CHANGELOG
- [ ] Run basic Swagger tests in Travis

Use spec at https://github.com/skycoin/libskycoin/blob/develop/lib/swagger/skycoin.v0.27.0.openapi.v2.yml