Change license to MIT
Fixes #7408 - added lazy loading of credentials

- credentials container abstract
- support API documentation (JSON) accessible without authentication
- RestClient connection initialized only when needed
- option to to use unauthenticated connection for method calls
Merge pull request #20 from mbacovsky/7408_lazy_credentials

Fixes #7408 - added lazy loading of credentials
Merge pull request #17 from mbacovsky/mit_license

Change license to MIT