add complete es5/es6 support

[pleerock]

Right now its possible to use validator with es5/es6, but we can provide more features to make this experience smoother. List of todos:

• add support of registering validation schema for target class
• add support of registering custom validations without using decorators
• make schema validation better
• cover schema validation with tests
• add samples with javascript, or javascript + babel + decorators?
• add docs how to use class-validator with javascript
• add docs how to use class-validator with system-js

[NoNameProvided]

Closing in favor of #178.