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
Add query helper to parse selection criteria
Add `select` clause to the criteria object

This commit adds a `select` clause to the criteria object which allows for
including only specific model attributes within the query result. It accepts
the follwing syntax:
  `.select(['attr1', 'attr2'])`
  `.select('attr1', 'attr2')`
  `.select({attr1: 1, attr2: 1})`
Add `prune` clause to the criteria object

This commit adds a `prune` clause to the criteria object which allows for
excluding model attributes from the query result. It accepts the follwing
syntax:
  `.prune(['attr1', 'attr2'])`
  `.prune('attr1', 'attr2')`
  `.prune({attr1: 1, attr2: 1})`
Add `select` and `prune` as operational keys
Add tests for `select` and `prune` operators