[WIP] Add List support for References Get #439

**Commit Comments:**
Added new test for a Get call for References that returns a list of objects
Updated the related methods to return the read only list of references
Updated the tests that were looking for a single reference to use the first index position
Updated the SimpleJSON DeserializeObject method to check the if the return type is a generic collection, or assignable form one, to create the List when only a single reference is returned
This was required because the API returns a single object from the Get method without the list wrapper if it only finds one

**Discussion Notes:**
The ObservableReferences Get most likely needs to change still.  It is not being flattened like the GetAll method
Array index notation is being used to grab the first element when other places were expecting a single reference.  Perhaps those should be changed as well?
Added a pull request to the Simple JSON Project as well at facebook-csharp-sdk/simple-json#63 for the deserialization changes I made to SimpleJSON.cs