Make field reference more flexible

Will need to support {"rtype": "restriction"} for turn
restriction field.

data/presets/fields.json

@@ -7,7 +7,9 @@
             "bicycle",
             "horse"
         ],
-        "referenceKey": "access",
+        "reference": {
+            "key": "access"
+        },
         "type": "access",
         "label": "Access",
         "placeholder": "Unknown",
@@ -66,7 +68,9 @@
             "addr:city",
             "addr:postcode"
         ],
-        "referenceKey": "addr",
+        "reference": {
+            "key": "addr"
+        },
         "icon": "address",
         "universal": true,
         "label": "Address",

data/presets/fields/access.json

@@ -1,6 +1,6 @@
 {
     "keys": ["access", "foot", "motor_vehicle", "bicycle", "horse"],
-    "referenceKey": "access",
+    "reference": {"key": "access"},
     "type": "access",
     "label": "Access",
     "placeholder": "Unknown",

data/presets/fields/address.json

@@ -6,7 +6,7 @@
         "addr:city",
         "addr:postcode"
     ],
-    "referenceKey": "addr",
+    "reference": {"key": "addr"},
     "icon": "address",
     "universal": true,
     "label": "Address",

data/presets/schema/field.json

@@ -14,9 +14,35 @@
                 "type": "string"
             }
         },
-        "referenceKey": {
-            "description": "Tag key which should be used to get taginfo documentation for (to be used when a field manages multiple tags)",
-            "type": "string"
+        "reference": {
+            "description": "Taginfo documentation parameters (to be used when a field manages multiple tags)",
+            "type": [
+                {
+                    "type": "object",
+                    "properties": {
+                        "key": {
+                            "description": "For documentation of a key",
+                            "type": "string",
+                            "required": true
+                        },
+                        "value": {
+                            "description": "For documentation of a tag (key and value)",
+                            "type": "string"
+                        }
+                    },
+                    "additionalProperties": false
+                },
+                {
+                    "type": "object",
+                    "properties": {
+                        "rtype": {
+                            "description": "For documentation of a relation type",
+                            "type": "string"
+                        }
+                    },
+                    "additionalProperties": false
+                }
+            ]
         },
         "type": {
             "description": "Type of field",

js/id/ui/preset.js

@@ -134,8 +134,7 @@ iD.ui.preset = function(context) {
                 return field.present();
             })
             .each(function(field) {
-                var key = field.referenceKey || field.key,
-                    reference = iD.ui.TagReference({key: key});
+                var reference = iD.ui.TagReference(field.reference || {key: field.key});
 
                 if (state === 'hover') {
                     reference.showing(false);