Flat field added to apartment building

data/presets/fields/building.json

@@ -5,4 +5,4 @@
     "terms": [
         "structure"
     ]
-}
+}

data/presets/fields/capacity.json

@@ -4,4 +4,4 @@
     "minValue": 0,
     "label": "Capacity",
     "placeholder": "50, 100, 200..."
-}
+}

data/presets/fields/flats.json

@@ -0,0 +1,7 @@
+{
+    "key": "flats",
+    "type": "number",
+    "minValue": 0,
+    "label": "Flats",
+    "placeholder": "2, 4, 6, 8..."
+}