CategoryOverpassFilter: translate placeholder

doc/Filters.md

@@ -36,6 +36,7 @@ Each filter can define the following values:
   * 'has_key_value' query object with a tag with this key
   * 'strsearch' query string parts (e.g. "kai keb" would match "Kaiser Kebap") and query character variants (e.g. "cafe" would match "café").
 * show_default: if true, this filter will be shown by default, others need to be added via the select box.
+* placeholder: a text which is shown as placeholder (Twig enabled)
 
 ### Values
 #### Array

src/CategoryOverpassFilter.js

@@ -121,6 +121,11 @@ class CategoryOverpassFilter {
           f.values = v
         }
       }
+
+      if ('placeholder' in f && typeof f.placeholder === 'string') {
+        let t = OverpassLayer.twig.twig({ data: f.placeholder, autoescape: true })
+        f.placeholder = decodeHTML(t.render({}).toString())
+      }
     }
 
     let masterOptions = {