Ingredient handling should deal with multiple things having the same name

[raacampbell]

Both with image stacks (#121) and sparse ingredients (#210) creating a new one will automatically over-write an old one of the same name. I think it's safest if Lasagna always identifies if this is the case and does this:

• Renames existing item to ITEM_01 from ITEM
• Renames new one to ITEM_02
• User tries to add a third ITEM it will be named ITEM
• A fourth will rename existing ITEM to ITEM_03 and newly loaded ITEM to ITEM_04

This should be in place in the main application's plugin handler. This way add_line_plugin doesn't have to do anything new and we also fix issue #121.