Make Waterline core validations "reserved / ignored properties" extendable

Pass a `defaults.validations` configuration object as additional argument to Validator.initialize() in the Waterline Core.

As `defaults` is already coming from sails.config.models, it seems a good idea to extend it there with a "validations" object holding the configuration for the model validator.
Added a test for validations with extra ignored properties.
Merge pull request #482 from mphasize/master

Make 'reserved keywords' in validations extendable