Enable easy launching of multiple modules from single script using roslaunch

[skugele]

Calling a script or program that spawns multiple processes from a element in a ROS launch file fails because ROS expects each to have a 1-to-1 mapping with a process.

If we don't want to structure our code to have a single script per module (which is annoying) then I think we will need to adopt a strategy similar to an earlier version of lidapy, which used command-line arguments to specify which module to launch in a multiple module script.

If someone has an alternate idea I am all ears... Otherwise, I am going to add some helper functions to lidapy to make supporting command-line arguments that launch a LIDA module easier.