grasp position detector: move robot specific parameters to robotpart attributes instead of arguments.

[PetervDooren]

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As discussed in https://github.com/tue-robotics/tue_robocup/pull/1239/files#r985110147 and https://github.com/tue-robotics/tue_robocup/pull/1239/files#r985110332, the grasp detector smach state has some magic numbers for the minimum joint position where detection is possible (i.e. fingers closed). However this value is robot specific. currently it is supplied as a default argument which can be changed by a user but this value should not change in between tries as it is tied to the robot. It would therefore make more sense to have it as an attribute of a robot part.