message: fix limits and simplify collision model
  The gripper fingers both can move 30mm according to the datasheet
  to give a distance of 60mm between the fingers.
  The _finger_palm_link can be easily simplified as a box geometry
  for faster collision checking.
diff: </geometry>
  </visual>
  <collision>
  + <origin xyz="0 0 ${0.040-0.5*0.0171}" rpy="0 0 0" />
  <geometry>
  - <mesh filename="package://schunk_description/meshes/pg70/pg70.stl" />
  + <box size="0.082 0.114 0.080" />
  </geometry>
  </collision>
  </link>
  <parent link="${name}_palm_link" />
  <child link="${name}_finger_left_link" />
  <axis xyz="0 1 0" />
  - <limit effort="10" lower="-0.001" upper="0.061" velocity="2.0"/>
  + <limit effort="10" lower="-0.001" upper="0.0301" velocity="0.041"/>
  </joint>
  <link name="${name}_finger_left_link">
  <child link="${name}_finger_right_link" />
  <axis xyz="0 -1 0" />
  <mimic joint="${name}_finger_left_joint" multiplier="1" offset="0"/>
  - <limit effort="10" lower="-0.001" upper="0.061" velocity="2.0"/>
  + <limit effort="10" lower="-0.001" upper="0.0301" velocity="0.041"/>
  </joint>
  <link name="${name}_finger_right_link">
  