Labels for relations between classes in classdiagrams

src/less/forest/classDiagram.less

@@ -15,6 +15,17 @@ g.classGroup line {
   stroke-width:1;
 }
 
+svg .classLabel .box {
+  stroke: none;
+  stroke-width:0;
+  fill: @nodeBkg;
+  opacity: 0.5;
+}
+
+svg .classLabel .label {
+  fill: @nodeBorder;
+}
+
 .relation {
   stroke: @nodeBorder;
   stroke-width: 1;