Issue #530: Add debug msg for Layout errors

New issue 530: Add debug messages for Layout creation errors https://bitbucket.org/valentinateam/valentina/issues/530/add-debug-messages-for-layout-creation

Susan Spencer:

When creating a Layout, users sometimes get the critical error message popup:

“Couldn’t prepare data for creation layout”

The debug log in Qt doesn’t generate any messages to assist with this error. Please implement debug messages for this error, indicating which aspect or which step of building the Layout failed.