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.
The thing is, this notice is cleared out just before the run, since prepareRun() is now called after the user makes a choice. Shall I still go ahead and delete the status messages though? It seems like they add a bit of not-so-necessary code.