Override check_origin and fix test suite

Starting with tornado 4.0 cross-rogin connections are refused by default.

As mentioned in the docs (http://www.tornadoweb.org/en/stable/websocket.html#tornado.websocket.WebSocketHandler.check_origin) overriding check_origin allows this behaviour to be changed

This pull request fixes #22

It also fixes the test suite to work correctly on TravisCI