[ros] fix get_time to properly use simulated timestamp
[middleware/socket] Allow user to specify wished port

Fix #493
[doc] Document the 'port' keyword accepted by socket mw
[doc] Document in release note the new keyword 'port' for socket datastream
[SemanticCamera] add a 'tag' property to select visible objects
[SemanticCamera] add a 'relative' property
[SemanticCamera] remove the try/except structure

suggested by Arnaud Degroote
[SemanticCamera] fix relative orientation
[Camera] fix camera frame transformation + relative in SemanticCamera

The frame of the camera, available using self.position_3d
is now computed using a frame transformation to be consistent
with MORSE conventions.

Also change the builder part, so that when doing:
robot = ATRV()
camera = VideoCamera()
robot.append(camera)

The camera is oriented the same way as the robot (regaring objets
themselves and their position_3d).
And robot.rotate and camera.rotate behave the same way.

SemanticCamera now uses transformations to compute the position
of detected objects in the camera frame.
[SemanticCamera] fix transformation relative to camera frame