Panel: Domain Items and Types should be links only if they don't already exist in domain

[bmcdougald]

If you open a page and click an extracted item to add it to the domain (while domain items toggle is set to on) it will highlight in the page AND the side panel (letting you know that that extracted item is "already a domain item" so you don't need to try and add it again. If you then go to a new page, the domain term will highlight on the page properly, but when the extracted items panel comes back it does not show the domain items that already exist as highlighted.

Since we do not disable or omit extracted items or types that are already added to the Domain, and we're not highlighting them to call attention to them already being part of the domain...it creates a situation where we can add the same term or type multiple times for the domain. This is less than desirable behavior.

[michaelsframe]

This original behavior was actually a bug. Revising title and functionality to reflect how it should work in new Firefox sidebar.

Domain Items and Domain Entity Types should only show as links if they do not already exist in the Domain. Once added they should be converted from links to labels.