Add preset for cemetery=sector (#517)

Also added fields for:
* `sector:name`
* a dedicated `ref` field labeled 'Section Number'

data/fields/ref_sector.json

@@ -0,0 +1,5 @@
+{
+    "key": "ref",
+    "type": "text",
+    "label": "Section Number"
+}

data/fields/sector/name.json

@@ -0,0 +1,6 @@
+{
+    "key": "sector:name",
+    "type": "text",
+    "label": "Name",
+    "placeholder": "Dedicated name (if any)"
+}

data/presets/cemetery/sector.json

@@ -0,0 +1,27 @@
+{
+    "icon": "maki-cemetery",
+    "fields": [
+        "sector/name",
+        "ref_sector"
+    ],
+    "geometry": [
+        "point",
+        "area"
+    ],
+    "tags": {
+        "cemetery": "sector"
+    },
+    "terms": [
+        "burial ground",
+        "cemetary",
+        "cemetery",
+        "cemetery section",
+        "churchyard",
+        "columbarium",
+        "grave yard",
+        "graveyard",
+        "mausoleum",
+        "tomb"
+    ],
+    "name": "Cemetery Section"
+}