Support for data classes/`NamedTuple`s

[khatchad]

We currently hit a parsing error when encountering a "data class" (introduced in Python 3.7). Here's an example:

https://github.com/kyzhouhzau/NLPGNN/blob/b9ecec2c6df1b3e40a54511366dcb6085cf90c34/nlpgnn/models/TextGCN2019.py#L12-L16

We're getting a front-end parsing error for this. Most likely, it would require a Jython change. To get more info, I filed https://github.com/jython/jython/issues/339.

[khatchad]

Actually, this is an example of a NamedTuple, which has a similar syntax.