Python3 support


I’ve converted Redash to support Python3 and Python2 for my own use (I’m connecting to Sqlite and Postgresql only at the moment). Just wondering how much interest there is out there for others to support this. At the moment the code is proof of concept, would need a lot more testing/review for production readiness.

A couple of dependencies needed to be upgraded (vertica, mysql, psaml), while pyhive, wsgiref support were dropped.