python: add qi.Future (for documentation and correctness purpose)
python: add qi.Future (for documentation and correctness purpose)

qi.Future cannot be instanciated.

Change-Id: I7a964594df9bd9f92d1a36eb13368756183574aa

bsautron/libqi,aldebaran/libqi,aldebaran/libqi,aldebaran/libqi,vbarbaresi/libqi