Fix httplib2 dependency check

- Move dependency check from threadedhttp.py to http.py
  and revise it removing the dependency on setuptools for
  running pywikibot (it is still required to use setup.py)
- Add httplib2 version checks, and display the httplib2 __file__
  to assist the user identify why they have the wrong version.

Bug: 66618
Change-Id: I66c9a42f80710dec78b6e2b25ccb7b4b949c5740
Merge "Fix httplib2 dependency check"