Merge: interactive nit: main variables are preserved

This hacks (by refinement) the scope and interpretation services to load and save the states of the local variables of the main method.

`nitin` is now usable for everyday usages:

~~~raw
-->var sum=0
-->for i in [0..5[ do
...print i
...sum += i
...end
0
1
2
3
4
-->print sum
10
~~~

Pull-Request: #2584