Specify in-place operators

The following operators have now an in-place ProdConso model:

• Flatten;
• Identity;
• Reshape;
• Squeeze;
• Unsqueeze.

This is important for the export memory manager, since by default, it uses the default operators implementation ProdConso model. Therefore, these operations will be nop in export because the output memory plane will be the same as the input one in most cases!