A bunch of fixes to express declaration

- Move Express-prefixed interface names into internal module as
  unprefixed names
- The importing code will use express.Response instead of
  ExpressServerResponse
- Internal definitions can just use Response instead of
  ExpressServerResponse
- Response should extend http.Response to be able to type check .end
  for example
Merge pull request #1077 from sgronblo/improve_express_d_ts

Namespacing for express definition