Tutorial - Add initial and final actions

[Neon22]

so that when tutorial begins - can maybe load a file. and when it ends then can put system back where it was...

Not sure if eval is the right thing to do here...?

[Neon22]

pretty sure eval() is not the right thing to do...

[laffra]

I think eval is not the right approach, indeed. You can make users pass a generic function and then call it inside the init and run methods? If you can make that change and submit again, I think this makes a lot of sense to merge into HEAD.