improve bridge visualisation

Signed-off-by: Michael Leuschel <leuschel@uni-duesseldorf.de>

Bridge/visb_m1.json

@@ -4,22 +4,22 @@
     {
       "id": "nr_cars_on_island",
       "attr": "text",
-      "value": "b"
+      "value": "FORMAT_TO_STRING(\"b=~w\",[b])"
     },
     {
       "id": "nr_cars_on_bridge_a",
       "attr": "text",
-      "value": "a"
+      "value": "FORMAT_TO_STRING(\"a=~w\",[a])"
     },
     {
       "id": "nr_cars_on_bridge_c",
       "attr": "text",
-      "value": "c"
+      "value": "FORMAT_TO_STRING(\"c=~w\",[c])"
     },
     {
       "id": "nr_cars_on_island_and_bridge",
       "attr": "text",
-      "value": "FORMAT_TO_STRING(\"~w/~w\",[n,d])"
+      "value": "FORMAT_TO_STRING(\"cars: ~w/~w\",[n,d])"
     },
     {
       "id": "IL",