Add a warning when attempting to close osci-render with unsaved changes

[jameshball]

Currently, you can easily make lots of changes and close the program after forgetting to save, losing your progress.

The program title currently updates to include "unsaved files" at the top, but this only updates when you edit a file, and not when you change a slider value, for example.

For a decent first version of this, you could simply detect when any slider value has changed and then update the title accordingly. Later iterations of this could include monitoring updates text fields, and settings in the bar at the top.

This could work by having the MainController listen to all sub-controllers and whenever a value is changed, tell the MainController.

When closing osci-render, first check if there are unsaved changes, and open a pop-up window asking the user if they want to save before exiting or not.