Rework Highlighting

Rework the broken highlighting feature.

1. Hovering over a node should increase its visibility. This can be done by highlighting all its edges, increasing its size (slightly), etc.
2. A selected node should be easier to see. All nodes that are not connected to the selected node should be grayed out (this can be done using CSS - see https://www.w3schools.com/howto/howto_css_image_bw.asp). In addition their names should be partially transparent.
3. Since selecting a node now has a greater influence, it should be possible to deselect a node, by both clicking into the background, or by closing the info area.