don't pass ItemPool to Item::itemProperty

The items this function creates should always go into the same
pool the item itself is in.

Change-Id: I36ba8543a545c11db40d2792f0f8f5833530bf32
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
rename ProductModule to Export

The name "Export" reflects the characteristics of this item better
than "ProductModule" and is also similar to what is used in other
build tools.

ProductModule is now deprecated.
Support for it will be removed in 0.5

Change-Id: I736d51f40e547ec38e3922c0793a7b57890ecd47
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>