Set Name field also for subtasks

At the moment it seems that the name of the subtask cannot be changed and it is always the key of the yaml

For example: 
```yaml
RightArm:
    type: "Cartesian"
    name: "right_arm"
    #distal_link: "arm2_8"

RightArmLinear:
    type: "Subtask"
    task: "RightArm"
```

Results in having the topics : 
```bash
/cartesian/right_arm/***
/cartesian/RightArmLinear/***
```


