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
(cherry picked from commit d688bbe3bc7c21e87e9dc625ae968449aa73f317)
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.
(cherry picked from commit 6559ac2486e37a7b534304021093121d8d40422b)