Introrob_py: improve interaction with real-Ar.Drone

Introrob currently has a limited control over the real-ARDrone. Is necessary add improvements to better control of the quadrotor.

[varhub]

Component roughly tested with under develop ardrone_server and gazebo. Working without problems.
Include patches from:

• Fix Python/Numpy future warning for img != None. #182 "Fix Python/Numpy future warning for img != None"
• Zero cmd_vel on takeoff, reset, and land. AutonomyLab/ardrone_autonomy#160 "Zero cmd_vel on takeoff, reset, and land"