Style areas on dashboard the same as alert preview

Our style for areas is pale blue background with black keylines or bold
black text.

This commit makes the display of area names on the dashboard consistent
with that visual style.

This also means that we’re not truncating the list of areas, which is
appropriate because no one area is more important than any of the
others.

app/models/broadcast_message.py

@@ -76,12 +76,6 @@ class BroadcastMessage(JSONModel):
             for parent in area.parents:
                 yield parent
 
-    @property
-    def initial_area_names(self):
-        return [
-            area.name for area in self.areas
-        ][:10]
-
     @cached_property
     def polygons(self):
         return Polygons(