#8 Add checks during iterations in debug mode only

[Muriel Salvan]

In debug mode, add tests to check values (exist and never greater). If these checks fail, it means that the assignment strategy class has a bug, and assigns resources it shouldn't.
In debug mode, check that the total assigned hours does not exceed the sizing. Otherwise it would mean the assignment strategy has assigned more resources than needed.

This is to be done in iterateOverAssignments