Add building:part field (#527)

data/fields/building/part.json

@@ -0,0 +1,6 @@
+{
+    "key": "building:part",
+    "type": "combo",
+    "default": "yes",
+    "label": "Building Part"
+}

data/presets/building_part.json

@@ -1,6 +1,7 @@
 {
     "icon": "maki-building",
     "fields": [
+        "building/part",
         "building/levels",
         "height",
         "building/material",