use amenity=dancing_school for Dance Studio, add field for dance:teaching

closes #373, see also #814

data/fields/dance/teaching.json

@@ -0,0 +1,5 @@
+{
+    "key": "dance:teaching",
+    "type": "check",
+    "label": "Offers Dance Lessons"
+}

data/presets/leisure/dance.json

@@ -6,7 +6,8 @@
         "address",
         "building_area_yes",
         "opening_hours",
-        "dance/style"
+        "dance/style",
+        "dance/teaching"
     ],
     "moreFields": [
         "email",

data/presets/leisure/dancing_school.json

@@ -29,12 +29,10 @@
         "dance teaching"
     ],
     "tags": {
-        "leisure": "dance",
-        "dance:teaching": "yes"
+        "amenity": "dancing_school"
     },
-    "reference": {
-        "key": "leisure",
-        "value": "dance"
-    },
-    "name": "Dance School"
+    "name": "Dance School",
+    "aliases": [
+        "Dance Studio"
+    ]
 }