[#43122757] introducing application settings
missing migration
defining settings as constants in the Setting class
Fix CI: Various tests

Fix CI: Modell.Modellzubehoer deaktivieren

Fix CI: Benutzer verwalten.Elemente der Benutzeradministration
[#43122757] introducing application settings
- fixing constants definition in Setting
- application#load_settings before_filter, where singleton are always required
- tests