VM: add some optional callbacks

Created by: retornaz

This commit add two callbacks, one which is called every time the VM get a "run" message, this enable to track each time the user hit the run button in asebastudio. The second one tracks each time the VM is encountering an user programming error, such as division by 0, out of array access or wrong native function use.

This is used on the next thymio II firmware. So please pull it or propose another way to have the same features :)