Extend homer_gesture_recognition Interface

Add some functions to interfaces.py:

• get_pointing_ray(): Waits for an actually intended gesture (multiple similar gesture recognitions)
• get_closest_object_to_pointing_ray(): Returns the closest object to a given pointing ray
• sort_objects_by_distance_to_pointing_ray(): Returns the sorted object list, sorted by ascending distance to pointing ray

merged

mentioned in commit 21f296d8