Feature: new launch file that splits domain and problem PDDL model file

[robodrome]

I would like a launch file that separates the domain PDDL and the problem PDDL.

I think this launch file can be adapted so split the model_file argument into two separate ones.

Does that make sense?

I can do it myself, but I would first like to know what others think about this.

[robodrome]

see my PR:
#274