Move object mapping to mainService DataService

[tejaede]

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[tejaede]

Latest commits add a couple of new features to the API.

1. DataService#batchAddsDataToStream is a boolean that allows defining whether the service adds mapped objects to the DataStream as soon as each is ready or waits for the entire batch of rawData to finish mapping before adding it to the DataStream.

2. PropertyDescriptor#isDerived allows defining whether a DataTrigger should return an in-process update on updateObjectProperty, if it exists.

*Note: PropertyDescriptor#isDerived existed but was unused as far as I could tell. I felt it accurately describes the new functionality and so I used it to avoid changes to the API surface.

For example, assume updateObjectProperties(myObject, "aProperty") below take a few seconds to resolve. This means that Update 2 will occur before Update 1 has resolved. Further explanation is in the comments

//Update 1
this.service.updateObjectProperties(myObject, "aProperty").then(function () {});

//Update 2
this.service.updateObjectProperties(myObject, "aProperty").then(function () {
     // If the propertyDescriptor of "aProperty" has isDerived = false (default), this update
     // will receive the same promise generated by Update 1.

     // If the propertyDescriptor of "aProperty" has isDerived = true, this update will kick off
     // a new fetch and generate a new promise. 
});

This name "isDerived" comes from the idea that a derived property's value is subject to change based on the criteria used to fetch it. By that logic, we cannot assume that two updateObjectProperties() for the same property return the same results, and therefore, we cannot return the same promise for 2 separate calls. In the future, we can improve on this by checking whether there were changes on the properties on which this property is derived.

@johnnykahalawai @marchant