Now prompts about losing changes on exit

... that's the change. Realised I hadn't accounted for that when I was dealing with saving changes, so the program now prompts when quitting that changes will be lost. There is a slight discrepancy in that it doesn't lead into a save dialog, because of the structure, but I'll iron that out at some point.

The next release will start including some actual new graph functionality, I think, as I reckon most of the main (basic) functionality is working. The only strange hiccup I've been noticing recently is extra nodes being created if you double-click too far away from existing nodes... need to look into that.

Updated Windows ".exe" included, for convenience.