This commit adds option to deactivate user to "Manage user" modal.
A modal is opened on clicking the option to confirm the deactivation
and the "Manage user" modal is closed.
The error from the server, if any, is shown in the modal itself
and in case deactivation is done successfully, the modal is closed.
Fixes#18944.
Moved `admin_human_form` template to `/templates/settings/` folder as
earlier, it was inaccurately placed within the `/templates` folder
and should have been within the `/templates/settings` folder.