Naming inconsistency

We have some confusing inconsistencies emerging that create build errors when expectation and usage doesn't coincide.

* Repo names use dashes (I think on all)
* Package names (in package.xml, cmake, setup.py, folders) sometimes use dashes, sometimes use underscores

I think the best practice here is to follow ROS convention. Use underscores *everywhere*. See [REP 0149#name](https://www.ros.org/reps/rep-0149.html#name). Dashes are permitted, but they are an exception to standard practice. You can see on the [foxy release page](http://repo.ros2.org/status_page/ros_foxy_default.html) that there is just one package that uses dashes.