New level and some minor improvements

Hello there!

Another update, new features!

Added:

• Button to toggle the grid to help count cells.
• New level (4th) with slightly more challenging task.
• There are unique initial scripts with short introductions for every level. In previous versions it was pretty much the same script.
• Short introduction in the last level because the scene is too large to show it with one camera angle.

So have fun and tell me what you think about it!