1. Rename the item classes based on their functionality.
Empty is explain the item visualization,
which is not proper to be understanding by user of this item.
using name of 'content', it explain what this item is purposed,
so let user using this item as 'container' of whole decoration.
2. Apply efl_part class for label and content.
we need to support specific efl_part for item to provide
easy binding data from the model in factory.