Add tool feature

[aaoliva]

This branch introduces the possibility to attach tools to the robot.

• Dynamic model updated and parametrized w.r.t. the tool parameters and gravitational acceleration.
• Kinematic model updates accordingly with the attached tool.
• The dynamic friction is simulated by subtracting the identified torque values to the joints.
• Franka Hand Gripper and some AprilTag model were added.
• Coppeliasim scene updated with new gripper model.
• Minor code clean-up.

[fspindle]

@aaoliva Thanks