add support for customize_task_weights in behaviors

[jbmouret]

Now in the YAML of the behavior, you can add customize_task_weights: and tune the weights. The rationale is that we sometimes want to deactivate some tasks in some behaviors (e.g. momentum in walk-on-spot).

Example:

BEHAVIOR:
  name : humanoid::clapping
  trajectory_duration : 1.0
  motion_size : 1.1
  customize_task_weights:
    com: 0.0

Do not abuse it!

It is difficult to customize more that the weights in a generic way:

• the size of masks depends on the task type
• the Kp are only for some tasks (e.g. SE3) and there is no generic interface

So, I'm not sure the added complexity / ugliness is worth it for the other parameters.