Split launch file for demo

[christianlandgraf]

A general idea to facilitate debugging and working with the real hardware: We may want to split the launch files into the general "bringup" part and the individual launch files to run tests and demos.

At the moment, this is becoming quite huge, and with the additional nodes for welding, it won't be any better...

[sjahr]

I've started with this but we need to discuss which launch files to split. My WIP can be found on sjahr/split_launch_files