Fix state properties cross reducer collision

[paradigm314]

Currently validstate combines reducers together into unified state to run validations. This will cause a collision if properties are named the name across multiple reducers such as:

• auth.email and contact.email

To resolve validstate_config should respect reducer namespaces and property keys should allow dot notation for access. IE

account: {
    'auth.name': { required: true },
    'auth.email': { email: true },
    'auth.password': { minLength: 8 },
  }

where auth is the key of the reducer inside of the combineReducers method.

[paradigm314]

In addition, to make syntax simple for single reducer validations a _reducer option should be added to define one reducer source. IE

account: {
    _reducer:  'auth',
    'name': { required: true },
    'email': { email: true },
    'password': { minLength: 8 },
  }

[paradigm314]

After talking through the implementation of this we have decided that it would be best to keep the interface consistent so the API will use _ values for reducer in the properties instead of dot notation like so:

account: {
    _reducer:  'auth',
    'name': { required: true },
    'email': { email: true },
    'password': { minLength: 8 },
    'paymentMethod: { required: true, _reducer: 'payments' }
  }

Where the property `_reducer` setting will override the overall validation setting. 
If a validation and property both are missing the `_reducer` key than a `ConfigurationError` should be thrown.