Previously validations were appended to an array when configured. The
format was cumbersome, and led to issues. This refactors the
configuration into an object, as a property of the Model.
Note that if no validations have been configured, this property is
currently `undefined`.
- change `statusCode` from 400 to 422
- nest `context` and `codes` inside `details`
- add `details.messages`
- reword the main error message
Remove the call to Error's constructor from ValidationError constructor,
because it's a no-op - Error's constructor creates a new
instance when called via `.call()`.
- Add a ModelDefinition class to encapsulate the model schema handling
- Add a Connector class as the base class for connector implementations
- Optimize attachTo and mixin
- Rename some properties/methods
Fabien Franzen
Raymond Feng
Miroslav Bajtos
Ritchie Martori
Anatoliy Chakkaev