ui: Add friendly date to Mailbox message view

- Refactor some date stuff

ui/src/Data/Date.elm

@@ -0,0 +1,21 @@
+module Data.Date exposing (..)
+
+import Date exposing (Date)
+import Json.Decode as Decode exposing (..)
+
+
+{-| Decode an ISO 8601 date
+-}
+date : Decoder Date
+date =
+    let
+        convert : String -> Decoder Date
+        convert raw =
+            case Date.fromString raw of
+                Ok date ->
+                    succeed date
+
+                Err error ->
+                    fail error
+    in
+        string |> andThen convert

ui/src/Data/Message.elm

@@ -1,5 +1,7 @@
 module Data.Message exposing (..)
 
+import Data.Date exposing (date)
+import Date exposing (Date)
 import Json.Decode as Decode exposing (..)
 import Json.Decode.Pipeline exposing (..)
 
@@ -10,7 +12,7 @@ type alias Message =
     , from : String
     , to : List String
     , subject : String
-    , date : String
+    , date : Date
     , size : Int
     , seen : Bool
     , text : String
@@ -34,7 +36,7 @@ decoder =
         |> optional "from" string ""
         |> required "to" (list string)
         |> optional "subject" string ""
-        |> required "date" string
+        |> required "date" date
         |> required "size" int
         |> required "seen" bool
         |> required "text" string

ui/src/Data/MessageHeader.elm

@@ -1,5 +1,6 @@
 module Data.MessageHeader exposing (..)
 
+import Data.Date exposing (date)
 import Date exposing (Date)
 import Json.Decode as Decode exposing (..)
 import Json.Decode.Pipeline exposing (..)
@@ -28,18 +29,3 @@ decoder =
         |> required "date" date
         |> required "size" int
         |> required "seen" bool
-
-
-date : Decoder Date
-date =
-    let
-        convert : String -> Decoder Date
-        convert raw =
-            case Date.fromString raw of
-                Ok date ->
-                    succeed date
-
-                Err error ->
-                    fail error
-    in
-        string |> andThen convert