Modify .gitignore to Ignore Things in "outputs" Directory

But it'll still pay attention to changes to "about_this_directory.txt"
Add caching to _run_the_experiment()

If an experiment and its settings are the same as the previous one, then
it's not re-run and only the results-displaying thing is called.
Move "R_script.r" into "scripts" Directory; WorkflowManager Uses It Better

- I renamed it to "scripts/R_bar_chart.r"
- the WorkM has a class property with the path to that script
- tests are updated to work with WorkM change
Fix Extension-Detection in WorkflowManager.export()

Now it'll properly detect if the provided pathname already has an
extension, and avoid adding a second one.