ui: Initial Elm UI import

Merged from https://github.com/jhillyerd/inbucket-elm

Uses https://github.com/halfzebra/create-elm-app

ui/src/Data/Session.elm

@@ -0,0 +1,91 @@
+module Data.Session
+    exposing
+        ( Session
+        , Persistent
+        , Msg(..)
+        , decoder
+        , decodeValueWithDefault
+        , init
+        , none
+        , update
+        )
+
+import Json.Decode as Decode exposing (..)
+import Json.Decode.Pipeline exposing (..)
+
+
+type alias Session =
+    { flash : String
+    , routing : Bool
+    , persistent : Persistent
+    }
+
+
+type alias Persistent =
+    { recentMailboxes : List String
+    }
+
+
+type Msg
+    = None
+    | SetFlash String
+    | ClearFlash
+    | DisableRouting
+    | EnableRouting
+    | AddRecent String
+
+
+init : Persistent -> Session
+init persistent =
+    Session "" True persistent
+
+
+update : Msg -> Session -> Session
+update msg session =
+    case msg of
+        None ->
+            session
+
+        SetFlash flash ->
+            { session | flash = flash }
+
+        ClearFlash ->
+            { session | flash = "" }
+
+        DisableRouting ->
+            { session | routing = False }
+
+        EnableRouting ->
+            { session | routing = True }
+
+        AddRecent mailbox ->
+            if List.head session.persistent.recentMailboxes == Just mailbox then
+                session
+            else
+                let
+                    recent =
+                        session.persistent.recentMailboxes
+                            |> List.filter ((/=) mailbox)
+                            |> List.take 7
+                            |> (::) mailbox
+
+                    persistent =
+                        session.persistent
+                in
+                    { session | persistent = { persistent | recentMailboxes = recent } }
+
+
+none : Msg
+none =
+    None
+
+
+decoder : Decoder Persistent
+decoder =
+    decode Persistent
+        |> optional "recentMailboxes" (list string) []
+
+
+decodeValueWithDefault : Value -> Persistent
+decodeValueWithDefault =
+    Decode.decodeValue decoder >> Result.withDefault { recentMailboxes = [] }