WIP Replace Tornado with asyncio and aiohttp

Replace Tornado with asyncio and aiohttp for our async and http client
needs:
    - aiohttp is significantly better than either of Tornado's
      httpclients, allowing the long-polling code to be simplified and
      keep-alive to be enabled (which will reduce disconnections and
      increase performance).
    - asyncio will make it easier for other projects to use hangups.

hangups now requires a development version of urwid with asyncio
support.