highlight block containing featured unit in medium view

fixes https://github.com/iqb-berlin/testcenter-frontend/issues/203

package.json

 {
   "name": "itc-ng",
-  "version": "5.0.3",
+  "version": "5.0.4",
   "license": "MIT",
   "repository": {
     "type": "git",

src/app/group-monitor/test-view/test-view.component.html

@@ -232,6 +232,7 @@
                         [class]="{
                             unit: true,
                             aggregated: true,
+                            current: true,
                             selected: selectedElement?.id === testletOrUnit.id,
                             marked: markedElement?.id === testletOrUnit.id
                         }"