Moved Flask-OAuth into lib/flask_oauth.py and using flask.ext.oauth for imports

No new versions or anything but moving the existing Flask extensions; to change the structure:

  * Moved the existing Flask-OAuth into `main/lib/flask_oauth.py` (instead of `main/lib/flaskext/oauth.py`)

  * This includes a file rename to `flask_oauth.py` compliant with the Flask-OAuth project naming of the same file (see https://github.com/mitsuhiko/flask-oauth/blob/master/flask_oauth.py)

For rationale and background see https://github.com/gae-init/gae-init/issues/48; which also describes that/how/why imports should use the `flask.ext.oauth` notation for Flask-OAuth (see `main/auth.py` for an example).