foxy support

[vinnnyr]

Addresses #13

• Change from rospy to rclpy in nodes, and src
• Message definitions now use std_msgs/Header
• CMake now uses ament_cmake and ament_cmake_python
• XML launch files tweaked to become compatible with Foxy
• Parameter files tweaked to be compatible with Foxy
• Dockerfile added, as well as instructions in README.md on how to build and pass HIDRAW through to the container

Test by using the Docker build instructions, source the underlay_ws, and do one of the three things: ros2 launch ds4_driver demo.launch.xml ros2 launch ds4_driver ds4_driver.launch.xml ros2 launch ds4_driver ds4_twist.launch.xml

The most significant changes needed were in the ds4_twist_node.py because of some changes in the way parameters are used.

[naoki-mizuno]

Thank you! I'd like to test this but I won't have access to a ROS2 environment in the next week or two, so I'll go ahead and merge it into foxy-devel.

[naoki-mizuno]

Merged into foxy-devel.