add "kerb" tag as an optional field to crossing vertices

when used without `barrier=kerb`, but on a crossing node.

fixes #858

see also https://wiki.openstreetmap.org/w/index.php?title=Key:kerb&oldid=2501049#By_itself

Author: tyrasd

data/presets/highway/crossing.json

@@ -7,7 +7,8 @@
         "crossing_raised"
     ],
     "moreFields": [
-        "flashing_lights"
+        "flashing_lights",
+        "kerb"
     ],
     "geometry": [
         "vertex"

data/presets/highway/crossing/_marked.json

@@ -7,9 +7,6 @@
         "crossing/markings",
         "crossing_raised"
     ],
-    "moreFields": [
-        "flashing_lights"
-    ],
     "geometry": [
         "vertex"
     ],

data/presets/highway/crossing/traffic_signals.json

@@ -11,6 +11,7 @@
         "traffic_signals/vibration"
     ],
     "moreFields": [
+        "kerb",
         "traffic_signals/arrow",
         "traffic_signals/countdown",
         "traffic_signals/minimap"

data/presets/highway/crossing/uncontrolled.json

@@ -7,9 +7,6 @@
         "crossing/markings_yes",
         "crossing_raised"
     ],
-    "moreFields": [
-        "flashing_lights"
-    ],
     "geometry": [
         "vertex"
     ],

data/presets/highway/crossing/unmarked.json

@@ -6,9 +6,6 @@
         "crossing/island",
         "crossing_raised"
     ],
-    "moreFields": [
-        "flashing_lights"
-    ],
     "geometry": [
         "vertex"
     ],

interim/source_strings.yaml

@@ -2711,6 +2711,7 @@ en:
       kerb:
         # kerb=*
         label: Curb
+        terms: '[translate with synonyms or related terms for ''Curb'', separated by commas]'
       kerb/height:
         # kerb:height=*
         label: Height