Switch to Tornado-Json Extension

[ayushr2]

We should probably switch to this extension: tornado-json
It enables us to define schemas, which leads to better error handling and simplifies the entire logic. Makes it easier to make JSON requests. Circumvents the annoying feature of tornado of providing all args as byte strings (which does not play well with python 3) and mess with lists. We will not have to urlencode and decode on both sides.