Remove indication of relationships.

Relationship lines are faint and unclear. Consider an alternative way of showing how points and shapes relate to one another. First, remove the current implementation.

- Remove shape paths for relationships.
- Remove UI button to toggle showing of relationships.
- Remove CSS for relationship lines.
- Also, make 2-arity call to `multipoint` function more transparent.

resources/public/css/taxicab.css

@@ -156,11 +156,6 @@ input[type=range]::-webkit-slider-thumb {
   height: 100%;
 }
 
-.relationship {
-  stroke: none;
-  fill: none;
-}
-
 #tools button {
   width: 95%;
 }
@@ -177,10 +172,6 @@ input[type=range]::-webkit-slider-thumb {
   cursor: crosshair;
 }
 
-#workspace[data-relationships=true] .relationship {
-  stroke: lightblue;
-}
-
 .grid {
   stroke: #ddd;
 }