Fix draggable trash item feature
Fix draggable trash item feature

Since the introduction of the nested elements feature this is broken, because the necessary `data-droppable-elements` attribute was missing on the "main content" cell div and had a duplicated `data-data` on the cells div.

AlchemyCMS/alchemy_cms,AlchemyCMS/alchemy_cms,robinboening/alchemy_cms,mamhoff/alchemy_cms,robinboening/alchemy_cms,mamhoff/alchemy_cms,robinboening/alchemy_cms,mamhoff/alchemy_cms,AlchemyCMS/alchemy_cms