Initial port to ROS 2

[chapulina]

I created the ros2 branch off master and I'm making this PR against it for visibility.

Noteworthy points:

• The drone_*.launch files have an undeclared dependency on the sitl_launcher, which is not available on dashing yet, so I left that launch file unported.

• The world files try to load a plugin that is not available on these packages, libgazebo_video_stream_widget.so, so that prints an error.

• Bumped all package versions to 2.0.0 to reserve 1.X for ROS 1

• Removed the env_hooks and used <export>s in package.xml instead.

Try it out

ros2 launch baylands baylands.launch.py

ros2 launch ksql_airport ksql.launch.py

ros2 launch mcmillan_airfield mcmillan.launch.py

ros2 launch sand_island sand_island.launch.py

ros2 launch yosemite_valley yosemite.launch.py

[ahcorde]

Closing this PR in favour of this one https://github.com/osrf/uav_testing/pull/8