introduce Rule.auxiliaryInputs

This eliminates the need of putting "hpp" into
Module.additionalProductFileTags to produce ui_XXX.h files.
Instead, we're making all hpp producing rules dependent on
the compiler rule.

Change-Id: I345cb3bee20d8080e40ca678d4db822ccd1af92e
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>