add preset for Variable Message Sign (#666)

data/presets/traffic_sign/variable_message.json

@@ -0,0 +1,18 @@
+{
+    "icon": "temaki-billboard",
+    "fields": [
+        "{traffic_sign}"
+    ],
+    "geometry": [
+        "point",
+        "vertex"
+    ],
+    "tags": {
+        "traffic_sign": "variable_message"
+    },
+    "terms": [
+        "vms",
+        "dynamic message sign"
+    ],
+    "name": "Variable Message Sign"
+}