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/NotificationGotifyForm.elm

@@ -0,0 +1,37 @@
+{-
+   Copyright 2020 Eike K. & Contributors
+
+   SPDX-License-Identifier: AGPL-3.0-or-later
+-}
+
+
+module Messages.Comp.NotificationGotifyForm exposing
+    ( Texts
+    , de
+    , gb
+    )
+
+import Messages.Basics
+
+
+type alias Texts =
+    { basics : Messages.Basics.Texts
+    , gotifyUrl : String
+    , appKey : String
+    }
+
+
+gb : Texts
+gb =
+    { basics = Messages.Basics.gb
+    , gotifyUrl = "Gotify URL"
+    , appKey = "App Key"
+    }
+
+
+de : Texts
+de =
+    { basics = Messages.Basics.de
+    , gotifyUrl = "Gotify URL"
+    , appKey = "App Key"
+    }