Changed default command scripting.

A very minor change, useful for the new tutorial: makes the default command scripting "echo Hello World!" instead of "echo Default command scripting".  The default command scripting used to print task ID information, but that is now done automatically for all tasks, in another job script section; so the actual content of the default "command scripting" item doesn't matter much.

@arjclark et.al. - please review.