Ui improvements

- don't show custom fields in edit menu if there are none. This
reduces load of ui elements. The first custom field must be created in
manage-data page.

- Add more validation to the money type

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

@@ -0,0 +1,43 @@
+module Data.Money exposing
+    ( Money
+    , format
+    , fromString
+    , roundMoney
+    )
+
+
+type alias Money =
+    Float
+
+
+fromString : String -> Result String Money
+fromString str =
+    let
+        points =
+            String.indexes "." str
+
+        len =
+            String.length str
+    in
+    case points of
+        index :: [] ->
+            if index == (len - 3) then
+                String.toFloat str
+                    |> Maybe.map Ok
+                    |> Maybe.withDefault (Err "Two digits required after the dot.")
+
+            else
+                Err ("Two digits required after the dot: " ++ str)
+
+        _ ->
+            Err "One single dot + digits required for money."
+
+
+format : Float -> String
+format money =
+    String.fromFloat (roundMoney money)
+
+
+roundMoney : Float -> Float
+roundMoney input =
+    (round (input * 100) |> toFloat) / 100