Display links between highlights and annotation blocks

When #34, #39 and the browsing panel container (#63) are done, add a simple view and a bunch of event handlers so that when both panel types are rendered side by side and an annotation on either side is hovered, the corresponding block/highlight on the other side is (also) emphasized and a (dotted) line is drawn between them to show that they belong together. See the dotted line in the image of #39 (cut-out below).