Add boilerplate for Google sign-in

For more information, read:
https://developers.google.com/identity/sign-in/web/sign-in?authuser=1

TODO: Use Elm ports or something similar to properly interop with the onSignIn
and signOn functions defined in index.html.

client/src/Login.elm

@@ -5,9 +5,12 @@ import Html.Attributes exposing (..)
 import Html.Events exposing (..)
 import State
 
+googleSignIn : Html State.Msg
+googleSignIn =
+    div [ class "g-signin2", attribute "onsuccess" "onSignIn" ] []
 
 render : State.Model -> Html State.Msg
 render model =
     div [ class "pt-10 pb-20 px-10" ]
-        [ p [] [ text "Please authenticate" ]
+        [ googleSignIn
         ]

client/src/State.elm

@@ -22,7 +22,7 @@ type alias Model =
 init : Model
 init =
     { isLoading = False
-    , view = Landing
+    , view = Login
     }