Deep refactoring to allow for different motor models in one DynamixelMotors object

[HanaeRateau]

This PR breaks the previous version of the API.

• Cleans the way the motor parameters are fetched using a catalog of all Dynamixel motors to load into ModelConfig class
• Introduces MotorConfig class to better manage motor configurations
• Introduces a flexible syntax to configure the gourp of motors with a dict or json file

Example of MotorConfig:

# Example of a motor description dictionary for 4 XM430-W210 motors, note that the IDs must be unique for each motor, but the other parameters can be shared among motors of the same model.
{
    "id": [0, 1, 2, 3],
    "model": "XM430-W210",
    "pulley_radius": 20,
    "pulse_center": 2048,
    "max_vel": 1000,
    "baud_rate": 57600
}

To do:

• Check the config with Alex
• Should we be able to have per-motor operating mode?
• Integrate the torque estimation functions