Added AutoSave feature as an enhancement

This consists of a pop-up, which includes a "Remember this decision" check-box, that pops-up every time the user tries to run a sketch that hasn't been saved, and gives the user the option of saving and running the sketch, or running it directly without saving.

However, the AutoSave feature has deliberately been left out for an untitled sketch, since untitled sketches are often used for prototyping.
`super.prepareRun();` should be called here. 
Are you getting the `run -> dialog prompt -> user clicks a button -> only then, sketch starts running` sequence with this code?
According to the current implementation, it seems to me, the sketch would start running, while the dialog is still displayed to the user, waiting for his response.