[feature suggestion] Make 'Add New Items' screen more informative by telling the user which items (plugins) are already installed

Currently: it grays out items that can't be added (because they were already added and can only have one instance, I assume) are grayed out.

It would be a good usability improvement if this screen would have textual descriptions towards the right of the list, like:

• already added and can only be added once
• already added once
• already added 3 times
• not added yet

Currently it is hard to find items that aren't already installed.