Prepare for selecting languages

UI language is stored in user settings for authenticated users;
otherwise is only stored in the current model (not persisted).

modules/webapp/src/main/elm/Messages/App.elm

@@ -0,0 +1,22 @@
+module Messages.App exposing
+    ( Texts
+    , de
+    , gb
+    )
+
+
+type alias Texts =
+    { login : String
+    }
+
+
+gb : Texts
+gb =
+    { login = "Login"
+    }
+
+
+de : Texts
+de =
+    { login = "Anmelden"
+    }

modules/webapp/src/main/elm/Messages/FixedDropdown.elm

@@ -0,0 +1,22 @@
+module Messages.FixedDropdown exposing
+    ( Texts
+    , de
+    , gb
+    )
+
+
+type alias Texts =
+    { select : String
+    }
+
+
+gb : Texts
+gb =
+    { select = "Select…"
+    }
+
+
+de : Texts
+de =
+    { select = "Auswahl…"
+    }

modules/webapp/src/main/elm/Messages/LoginPage.elm

@@ -0,0 +1,57 @@
+module Messages.LoginPage exposing
+    ( Texts
+    , de
+    , fr
+    , gb
+    )
+
+
+type alias Texts =
+    { username : String
+    , password : String
+    , loginPlaceholder : String
+    , passwordPlaceholder : String
+    , loginButton : String
+    , loginSuccessful : String
+    , noAccount : String
+    , signupLink : String
+    }
+
+
+gb : Texts
+gb =
+    { username = "Username"
+    , password = "Password"
+    , loginPlaceholder = "Login"
+    , passwordPlaceholder = "Password"
+    , loginButton = "Login"
+    , loginSuccessful = "Login successful"
+    , noAccount = "No account?"
+    , signupLink = "Sign up!"
+    }
+
+
+de : Texts
+de =
+    { username = "Benutzer"
+    , password = "Passwort"
+    , loginPlaceholder = "Benutzer"
+    , passwordPlaceholder = "Passwort"
+    , loginButton = "Anmelden"
+    , loginSuccessful = "Anmeldung erfolgreich"
+    , noAccount = "Kein Konto?"
+    , signupLink = "Hier registrieren!"
+    }
+
+
+fr : Texts
+fr =
+    { username = "Identifiant"
+    , password = "Mot de passe"
+    , loginPlaceholder = "Utilisateur"
+    , passwordPlaceholder = "Mot de passe"
+    , loginButton = "Connexion"
+    , loginSuccessful = "Identification réussie"
+    , noAccount = "Pas de compte ?"
+    , signupLink = "S'inscrire"
+    }