Add Apache-2.0 license headers

..._control/include/franka_control/franka_state_controller.h

franka_control/include/franka_control/services.h

franka_control/src/franka_control_node.cpp

franka_control/src/franka_state_controller.cpp

franka_control/src/services.cpp

...a_example_controllers/cartesian_pose_example_controller.h

...ample_controllers/cartesian_velocity_example_controller.h

..._example_controllers/joint_impedance_example_controller.h

...a_example_controllers/joint_position_example_controller.h

...a_example_controllers/joint_velocity_example_controller.h

...ude/franka_example_controllers/model_example_controller.h

...ple_controllers/src/cartesian_pose_example_controller.cpp

...controllers/src/cartesian_velocity_example_controller.cpp

...le_controllers/src/joint_impedance_example_controller.cpp

...ple_controllers/src/joint_position_example_controller.cpp

...ple_controllers/src/joint_velocity_example_controller.cpp

franka_example_controllers/src/model_example_controller.cpp

franka_gripper/include/franka_gripper/franka_gripper.h

franka_gripper/src/franka_gripper.cpp

franka_gripper/src/franka_gripper_node.cpp