Add helper function to add response

[hezronkimutai]

In the generated app, we have similar code blocks which could be instead kept in a function so as to increase the maintainability of the generated app. an example of such code block is

res.status(400).send({
     message: "An error occurred while creating user"
});

[ezkemboi]

@hezronkimutai, were we able to merge this into the master, please do confirm so that we can close the issue.

[ezkemboi]

Already solved.