This brings most of the history-related functionality implemented in the grpc scripts to the JSON version, but only for text output. It also renames parserJsonHistory.py to dish_json_text.py, which removes the last remaining complaint from pylint about module name not conforming to style conventions.
A lot of this is just duplicated code from dish_common and dish_grpc_text, just simplified a little where some of the flexibility wasn't needed.
This removes compatibility with Python 2.7, because I didn't feel like reimplementing statistics.pstdev and didn't think such compatibility was particularly important.
