add field for building:colour tag, closes #904

data/fields/building/colour.json

@@ -0,0 +1,9 @@
+{
+    "key": "building:colour",
+    "type": "colour",
+    "label": "Façade Color",
+    "terms": [
+        "building color",
+        "facade color"
+    ]
+}

data/presets/building.json

@@ -9,6 +9,7 @@
     ],
     "moreFields": [
         "architect",
+        "building/colour",
         "building/levels/underground",
         "building/material",
         "building/prefabricated",

data/presets/building_part.json

@@ -5,6 +5,7 @@
         "building/levels",
         "height",
         "building/material",
+        "building/colour",
         "roof/colour"
     ],
     "moreFields": [