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.
Why? Wouldn't it suffice calling prepareRun() once?

This is all that prepareRun() does:

`  public void prepareRun() {
    internalCloseRunner(); // Halts current runner
    statusEmpty(); // Clears status area
    for (int i = 0; i < 10; i++) System.out.println(); // advance/clear the terminal window / dos prompt / etc

    // clear the console on each run, unless the user doesn't want to
    if (Preferences.getBoolean("console.auto_clear")) {
      console.clear();
    }

    sketch.ensureExistence();     // make sure the user didn't hide the sketch folder

    sketch.getCurrentCode().setProgram(getText());

  }`