feat(messages): add html formatting to messages

This commit allows users to use the trix editor to send
messages with basic formatting and attachements.

* add active storage
* add actiontext
* add richtext field to messages
* add imageprocessing for message attachements
* add html email layout and adjust translations to use html urls

plugins/messages/config/locales/de.yml

@@ -138,6 +138,9 @@ de:
         Antworten: %{reply_url}
         Nachricht online einsehen: %{msg_url}
         Nachrichten-Einstellungen: %{profile_url}
+      reply: Antworten
+      see_message_online: Nachricht online einsehen
+      messaging_options: Nachrichten-Einstellungen
       footer_group: |
         Gesendet an Gruppe: %{group}
   navigation: