Fix inline tag help for fields that handle multiple tags

Some preset fields like the access-restriction field manage
multiple tags at once (access=*, foot=*, bicycle=*, …). Then
iD wasn't able to show inline help when clicking the ⓘ button.

This introduces a new parameter for these kind of fields:
`referenceKey` determines the tag key which should be used to
search taginfo documentation for.

Fixes #2222.

data/presets/fields.json

@@ -7,6 +7,7 @@
             "bicycle",
             "horse"
         ],
+        "referenceKey": "access",
         "type": "access",
         "label": "Access",
         "placeholder": "Unknown",
@@ -65,6 +66,7 @@
             "addr:city",
             "addr:postcode"
         ],
+        "referenceKey": "addr",
         "icon": "address",
         "universal": true,
         "label": "Address",

data/presets/fields/access.json

@@ -1,5 +1,6 @@
 {
     "keys": ["access", "foot", "motor_vehicle", "bicycle", "horse"],
+    "referenceKey": "access",
     "type": "access",
     "label": "Access",
     "placeholder": "Unknown",

data/presets/fields/address.json

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

data/presets/schema/field.json

@@ -14,6 +14,10 @@
                 "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"
+        },
         "type": {
             "description": "Type of field",
             "type": "string",

js/id/ui/preset.js

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