It might be useful to allow the user to specify that stdout is written to a file.

This could of course be achieved by creating a script to redirect the output, but it would be simpler for the user if the sampler did this.

Likewise for stderr and stdin.

If not specified, stderr and stdin are captured by the sampler as the sampler output.

Might also be worth considering supporting environment updates via ProcessBuilder#environment(). This would require an additional table on the GUI.