Support nested objects and arrays for GeoJSON features in query*Features

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**v0.16.0**:

Hi! This is my first issue report, so I hope I get it right.

Basically I'm trying to use the function queryRenderedFeatures to get the underlying data in JSON format to present on a popup. This works for the higher level of the JSON data (I can show the data on the popup), but fails to get the more deeply nested data - a console.log suggests that the objects have been converted into a string instead.

Here's the link to the issue as demonstrated using the example on "popup on hover": [jsbin](https://jsbin.com/leroki/edit?html,console,output)

I've edited the data such that there is only a single marker and also added an array of objects called "list" under "properties" a la feature.properties.list. I've also changed the popup HTML to display the first element of what is supposed to be a list.
### Expected Behavior

I expect that on hover the popup should display the first object, {"id":1,"name":"A"}.
### Actual Behavior

Instead, it shows "[", which confirms that it returns a string instead of the object.

Reproduce the behavior with the linked jsbin and the popup-on-hover example, starting at the queryRenderedFeatures API. Trace how feature.properties values are returned and verify that nested objects and arrays remain structured; done means the popup displays the first list object as {"id":1,"name":"A"} rather than "[".

Written by the indexing model from the issue text.