fitProperty should be an instance of EnumerationProperty

[pixelzoom]

Related to #143 code review.

In CurveFittingModel, this should be an EnumerationProperty:

      // @public {Property.<FitType>}, the method of fitting the curve to data points
      this.fitProperty = new Property( FitType.BEST, { validValues: FitType.VALUES } );

I.e.:

      // @public the method of fitting the curve to data points
      this.fitProperty = new EnumerationProperty( FitType, FitType.BEST );

[SaurabhTotey]

Sounds good, I'll get on that. Perhaps the documentation here https://github.com/phetsims/phet-core/blob/master/js/Enumeration.js#L40-L44 should be updated as well then.

[SaurabhTotey]

I have made the change for CurveFittingModel. Assigning to @pixelzoom to review.

[pixelzoom]

👍 Commit looks good.

I don't think the documentation for Enumeration should say anything about EnumerationProperty, for the same reason that Vector2 shouldn't say anything about Vector2Property. Those classes are values, and their API and doc shouldn't know anything about Property.