Launch two arms with wam7_sim

Modified launch files and urdf to make them more general, added lua script for second arm.
Does it make sense to expose all of these as arguments to the launchfile? It looks like it prevents you from having two arms with different initial positions / end-effectors. Maybe a good practice should just be to have an example 2-arm launchfile which people can use as a reference for various applications, instead of having one that they're meant to include.