Add catkin_package call to CMakeLists.txt

If a package lists the buildtool as `catkin` in the `package.xml`, it must call `catkin_package` in the `CMakeLists.txt`.

The alternative is to make the package a plain `cmake` package and then add instructions to your `CMakeLists.txt` to install the `package.xml` manually. Either way, the `package.xml` needs to be installed.

See https://github.com/ros/catkin/issues/622

Thanks!