Replace Express APIs removed in Express 5

Replaces app.del(...) with app.delete(...), res.sendfile(...) with res.sendFile(...), res.json(status, body), res.send(status, body) and res.jsonp(status, body) with res.status(status).json(body) (and likewise), res.json(body, status) with a numeric status second argument the same way, and res.redirect('back') with res.redirect(req.get('Referrer') || '/'). Only files that import or require express are changed. An application is a variable assigned express() or express.Router() in the same file, and a response is the second parameter of the enclosing function; the match is by name, not by type, so an application or response that comes from elsewhere is left alone. res.redirect('back') is changed only when the first parameter is available as req.