Duplicated instantiation of Guides

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For #374

Duplication in ArrowObjectScene and FramedObjectScene. The only thing that differs is the object arguments and phetioDocumentation.

    // Guides
    if ( optic instanceof Lens ) {
      this.guides1 = new Guides( this.optic, this.framedObject.positionProperty, {
        tandem: providedOptions.tandem.createTandem( 'guides1' ),
        phetioDocumentation: 'guides associated with the first point-of-interest on the framed object'
      } );
      this.guides2 = new Guides( this.optic, this.secondPoint.positionProperty, {
        tandem: providedOptions.tandem.createTandem( 'guides2' ),
        phetioDocumentation: 'guides associated with the second point-of-interest on the framed object'
      } );
    }
    else {
      this.guides1 = null;
      this.guides2 = null;
    }

[pixelzoom]

This turned into a bit of a mess -- doable, but at the expense of code readability. The optical objects are created by the subclass, and their positions are need to instantiate the guides. in the case of secondPoint, it's not really an optical object, just a position.

So at the expense of a few lines of duplicated code, I think it's best to keep things as is. The base class is responsible for creating things that are related to the optic. The subclasses are responsible for everything else.