Add tasks for all the new languages

Task/Reverse-a-string/Elm/reverse-a-string.elm

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+-- The import on the next line provides the reverse string
+-- functionality satisfying the rosettacode.org task description.
+import String exposing (reverse)
+
+-- The rest is fairly boilerplate code demonstrating
+-- interactively that the reverse function works.
+import Html exposing (Html, Attribute, text, div, input)
+import Html.Attributes exposing (placeholder, value, style)
+import Html.Events exposing (on, targetValue)
+import Html.App exposing (beginnerProgram)
+
+main = beginnerProgram { model = "", view = view, update = update }
+
+update newStr oldStr = newStr
+
+view : String -> Html String
+view forward =
+  div []
+    ([ input
+        [ placeholder "Enter a string to be reversed."
+        , value forward
+        , on "input" targetValue
+        , myStyle
+        ]
+        []
+     ] ++
+     [ let backward = reverse forward
+       in div [ myStyle] [text backward]
+     ])
+
+myStyle : Attribute msg
+myStyle =
+  style
+    [ ("width", "100%")
+    , ("height", "20px")
+    , ("padding", "5px 0 0 5px")
+    , ("font-size", "1em")
+    , ("text-align", "left")
+    ]