change launch file location

currently launch files are located under launch/ directory but when it is installed, they copy under capture_data directory, and downstream packages uses launch files under capture_data, not launch (https://github.com/mikeferguson/maxwell/blob/sixdof/maxwell_calibration/capture_data/capture_data.launch)

This means that this package will not work on devel setup, you have to catkin_make install to use this package. So this PR moves launch files under capture_data so that you can use both devel and installed situation.