Use an enum instead of a boolean to differentiate search

It's not very likely to have more modes of search besides normal and
trashed, but got surprised in that way quite often and it's nicer this
way anyways.

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

@@ -79,7 +79,7 @@ request mq =
     , limit = Nothing
     , withDetails = Just True
     , query = renderMaybe mq
-    , deleted = Just False
+    , searchMode = Nothing
     }