Automatic sorting of the added scripts
When scripts are added to an almost empty stack (1 or less element), the stack should be automatically sorted. If their is more elements, the new scripts should be sorted themselves, then added to the end of the stack.
Use biseau.sort_scripts_per_dependancies
function to get a new list of Script instance reordered according to their I/O.
A button in the GUI should also allow the user to apply this function on the full stack.