Enable power search for power users via ui settings

A different search bar is presented if enabled in ui settings that
allows to search via the new query language.

modules/webapp/src/main/elm/Data/ItemQuery.elm

@@ -52,6 +52,7 @@ type ItemQuery
     | ItemName AttrMatch String
     | AllNames String
     | Contents String
+    | Fragment String
 
 
 and : List (Maybe ItemQuery) -> Maybe ItemQuery
@@ -176,6 +177,9 @@ render q =
         Contents str ->
             "content:" ++ quoteStr str
 
+        Fragment str ->
+            "(& " ++ str ++ " )"
+
 
 attrMatch : AttrMatch -> String
 attrMatch am =