[TASK] Remove module Composer as such

The module must be intergrated by extending existing Vidi modules
Ex: FE User module must provide additional buttons for sending messages
[TASK] Adjust settings in the Extension Manager
[TASK] Remove legacy code

Remove the List Manager as implemented. It should be re-implemented
by extending a Vidi module which would then have all the benefit of
the Vidi Grid (multi-search, ...)
[BUGFIX] Fix saving of settings in Extension Manager