Language chooser in the UI
WiP on selectable mosaico templates. TODO: Make files always point to trusted URL, such that we don't have to rebase them. They are public anyway. The same goes for mosaico endpoints: /mosaico/templates and /mosaico/img
TODO: - format data based on field info in listDTAjax - integrate with the whole subscription machinery
some cleanup of models - handling dependencies in delete
