Allow deserialization of dateTime values to strings instead of DateTime objects when extracting such with JSONPath.

When a dateTime value is returned in a JSON response ("2019-04-08T00:00:00") and a JSONPath expression is used to extract it from that response, Test Studio deserializes it to a DateTime object. This leads to losing its original format. 

It will be useful to have the option to deserialize it in a plain string value.