incomplete implementation of SingleBulbPhotonBeamIO

[pixelzoom]

This looks like trouble in SingleBulbPhotonBeamIO:

    /**
     * Serializes an instance.
     * @returns {Object}
     */
    toStateObject: function() {
      return {};
    },

    /**
     * Deserializes an instance.
     * @returns {}
     */
    fromStateObject: function() {
      return {};
    },

    /**
     */
    setValue: function() {
    }

[samreid]

It looks like those methods are not necessary, we can opt out of the state altogether and still be a container for addChildInstance, fixed in preceding commit. @pixelzoom would you like to review? Close if all is well.