need confirmation to delete data-source from data-template

[shanekennedy]

when clicking on a data-source-item tab under a data-template, one might accidently click the red X & delete that data-source-item. there is no request for delete confirmation & a save is not required for this deletion.

adding the item back is simple, but you also have to re-associate the graph-input-field in the graph-management section for every device you have using this data source.