A way to view reciprocal links when card-editing

[jkomoros]

For example, in a recent change, see-also references in the info-panel show up whether it's an inbound or outbound link. This is nice, but it can mean that you go to edit a card that has a see-also... and then it doesn't have it, it's the other card. This can be very confusing.

For reference-types that are marked reciprocal, render shaded out/disabled tags in card-editor for inbound ones, and alert when you click on them.

Noticed while working on #670.