Add support for more generic notification

This is a start to have different kinds of notifications. It is
possible to be notified via e-mail, matrix or gotify. It also extends
the current "periodic query" for due items by allowing notification
over different channels. A "generic periodic query" variant is added
as well.

modules/webapp/src/main/elm/Messages/Comp/EventSample.elm

@@ -0,0 +1,40 @@
+{-
+   Copyright 2020 Eike K. & Contributors
+
+   SPDX-License-Identifier: AGPL-3.0-or-later
+-}
+
+
+module Messages.Comp.EventSample exposing
+    ( Texts
+    , de
+    , gb
+    )
+
+import Data.EventType exposing (EventType)
+import Http
+import Messages.Comp.HttpError
+import Messages.Data.EventType
+
+
+type alias Texts =
+    { eventType : EventType -> Messages.Data.EventType.Texts
+    , httpError : Http.Error -> String
+    , selectEvent : String
+    }
+
+
+gb : Texts
+gb =
+    { eventType = Messages.Data.EventType.gb
+    , httpError = Messages.Comp.HttpError.gb
+    , selectEvent = "Select event…"
+    }
+
+
+de : Texts
+de =
+    { eventType = Messages.Data.EventType.de
+    , httpError = Messages.Comp.HttpError.de
+    , selectEvent = "Ereignis wählen…"
+    }