AloTransform : probabilistic same_on_sequence and same_on_frames

[jsalotti]

In alodataset.transform.AloTransform, we can define the behavior of the transform with its boolean parameters :

• same_on_sequence
• same_on_frames

We should allow these parameters to take float values between 0 and 1, representing the probability to apply the same transformation or not.

At each call to the transform, a random draw (respecting the probabilities), to decide if the transform will be the same (on sequence and on frame)